DOL Wage and Hour API: WHD Opinion Letters and the Field Operations Handbook

The Department of Labor's Wage and Hour Division publishes two document sets that wage-and-hour software keeps needing and rarely has in structured form. Vaquill AI's US primary law API serves both under corpusType=AGENCY_GUIDANCE, separated by the source filter: whd_opinion_letter for the Division's written answers to specific fact patterns, and whd_foh for the Field Operations Handbook, the manual WHD investigators work from. Neither is a statute and neither is a regulation. The FLSA is at 29 U.S.C. 201 and following, the rules are at 29 C.F.R., and both of these sit below them. What makes the opinion letters worth a separate source code is 29 U.S.C. 259, which lets an employer plead good-faith reliance on a written interpretation of the Wage and Hour Administrator as a defense to a minimum wage or overtime claim.

Reviewed and corrected on 12 October 2026. This is general information, not legal advice.

TL;DR

• Two source codes, one corpusType. whd_opinion_letter and whd_foh both sit under corpusType=AGENCY_GUIDANCE and are filtered apart with source. Every result carries its own source, so a hit's value can be passed straight back as a filter.
• An opinion letter is WHD's answer to one requester's stated facts. It binds the Division's own enforcement posture. It is not law, and a court is not bound by it.
• 29 U.S.C. 259 is why the date matters. An employer that pleads and proves it acted in good faith in conformity with and in reliance on a written interpretation of the Administrator of the Wage and Hour Division has a bar to a claim for unpaid minimum wages or overtime under the FLSA, and the statute keeps that defense even where the interpretation is later modified, rescinded or held invalid.
• The Field Operations Handbook is internal enforcement procedure, not law. WHD says so on its own pages, and goodLawStatus on this source is unknown.
• Withdrawal is a real, machine-readable signal here, which is unusual for sub-regulatory guidance. actStatus for opinion letters is read off DOL's own footnote table rather than inferred.
• Coverage published on GET /us/statutes/coverage, which is the authoritative counter and costs no credits.

The wage-and-hour entry in our federal agency guidance series.

For related coverage, see Federal Agency Guidance API: 53 Sub-Regulatory Sources in One Endpoint for the corpus these two sources sit in, NLRB Memoranda API for the other federal labor-enforcement guidance layer, and Legal Data Provenance for where the text comes from.

The two sources

Those two descriptions are quoted verbatim from the source parameter documentation in the deployed spec at https://api.vaquill.ai/external/openapi.json, which is public and needs no key. The source enum carries 79 values in total, and an unrecognized value is rejected with a 422 rather than silently matching nothing.

What an opinion letter actually is

A person or firm writes to the Wage and Hour Division setting out a concrete situation. The Division writes back stating how it reads the FLSA, the FMLA, the Service Contract Act, the Davis-Bacon and Related Acts, the Consumer Credit Protection Act wage-garnishment provisions, or the Migrant and Seasonal Agricultural Worker Protection Act on those facts.

That is a narrower document than a regulation and a wider one than a private answer, because WHD publishes it.

Why 29 U.S.C. 259 makes these different from ordinary guidance

Most sub-regulatory guidance is persuasive and nothing more. Wage-and-hour guidance has a statutory hook.

Section 10 of the Portal-to-Portal Act, codified at 29 U.S.C. 259(a), says an employer is not subject to liability for failing to pay minimum wages or overtime under the FLSA, the Walsh-Healey Act or the Bacon-Davis Act if it "pleads and proves that the act or omission complained of was in good faith in conformity with and in reliance on any written administrative regulation, order, ruling, approval, or interpretation" of the agency named in subsection (b), which for the FLSA is the Administrator of the Wage and Hour Division and for the other two Acts is the Secretary of Labor. The statute also covers an "administrative practice or enforcement policy" of that agency. If the defense is established it is "a bar to the action," even if the ruling or interpretation is afterwards modified, rescinded, or determined to be invalid (29 U.S.C. 259).

DOL's own guidance page adds limits. It says rulings and interpretations issued by the Administrator under the FLSA, the Davis-Bacon Act or the Walsh-Healey Public Contracts Act are official rulings for purposes of the Portal-to-Portal Act, that letters signed by other WHD officials (marked NA) are official statements of WHD policy but are not rulings or interpretations under that Act, and that, with exceptions, the Portal-to-Portal Act does not apply to the FMLA or the other statutes WHD enforces (DOL, Final Rulings and Opinion Letters). A letter on the FMLA or on wage garnishment is persuasive guidance, but it does not carry this defense.

Two consequences for anyone building on this data.

1. The document is legally operative in a way a policy memo is not, so serving the wrong text is not a cosmetic error.
2. Reliance is evaluated as of a date. What matters is what the Division had published when the employer acted, which is why a corpus that serves today's text alone would fall short on this question and why the date handling below matters.

A short history: from a pottery plant to a good-faith defense

The reliance defense has a backstory, and it starts at a pottery plant. In Anderson v. Mt. Clemens Pottery Co., decided June 10, 1946, employees punched time clocks up to 14 minutes before the official start, walked to their work stations, and were paid only from the next even quarter hour. An employee could be credited with as much as 56 minutes a day less than the clock recorded, and the workers sued under the FLSA for overtime (Mt. Clemens).

Less than a year later, on May 14, 1947, Congress passed the Portal-to-Portal Act. Its opening section reads like a scolding. Congress found that the FLSA had been interpreted judicially "in disregard of long-established customs, practices, and contracts between employers and employees," creating "wholly unexpected liabilities, immense in amount and retroactive in operation" (61 Stat. 84). The Act did two things that matter here. It took "preliminary" and "postliminary" activities, such as the walk to the work site, out of FLSA liability. And in section 10 it gave employers the good-faith reliance defense that this post keeps coming back to.

That 1947 law is still deciding cases. On December 9, 2014 the Supreme Court held in Integrity Staffing Solutions v. Busk that roughly 25 minutes a day that warehouse workers spent waiting for and going through security screenings was not compensable. The Court said the screenings were postliminary, and noted that the result was consistent with a 1951 Department of Labor opinion letter that found a preshift safety screening and a postshift theft search noncompensable (Busk). So a 1951 opinion letter was still being cited by the Supreme Court in 2014.

People noticed. In an October 2019 Hacker News thread about the Supreme Court turning away an Amazon warehouse worker's wage appeal, one commenter who had read the Busk ruling wrote that "the blame for their not having to do so lies with the federal government's inability to update a 1947 law rather than with the courts" (hypersoar, Hacker News, October 2019). You may or may not agree with the policy. The comment does show how long a statute's shadow can run.

The opinion letter program has had its own ups and downs, covered in the status section below. In its most recent turn, the Department of Labor announced on June 2, 2025 that it was launching its opinion letter program across five enforcement agencies, with the Wage and Hour Division issuing opinion letters (DOL news release).

The Field Operations Handbook is procedure, not law

The FOH is how the Wage and Hour Division instructs its own investigators to read the FLSA, FMLA, SCA, DBRA, CCPA, MSPA and section 14(c), at a level of operational detail the regulations do not reach.

That makes it extremely useful for predicting what an investigator will do and completely wrong to cite as authority.

WHD says as much on its own pages: the handbook is an operations manual for investigators and staff, DOL publishes it under its FOIA obligation to make staff manuals public, the material may not reflect current legislation, regulations or significant court decisions, and the Federal Register and the Code of Federal Regulations remain the official resources (DOL, Field Operations Handbook). The corpus carries that as goodLawStatus: unknown rather than defaulting the source to in force.

What the Supreme Court said about letters and manuals

The cleanest statement of weight comes from a case about county deputy sheriffs. In Christensen v. Harris County, decided May 1, 2000, Harris County had worried about paying out accrued compensatory time, so it wrote to the Wage and Hour Division asking whether the sheriff could schedule employees to use it. The Acting Administrator answered in a September 14, 1992 opinion letter that, absent an agreement, neither the statute nor the regulations let an employer require it. The county adopted a policy requiring employees to use compensatory time anyway. The 127 deputies sued and asked the Supreme Court to defer to the letter. It sided with the county.

On the letter's weight, the Court wrote that opinion letters, "like interpretations contained in policy statements, agency manuals, and enforcement guidelines, all of which lack the force of law," do not get Chevron-style deference, and are "entitled to respect" only to the extent that they persuade (Christensen v. Harris County). The Chevron part of that has since changed, because the Court overruled Chevron in Loper Bright in 2024. The persuasion standard it points to is the older Skidmore test, and that one is still standing.

Read the quote with the handbook in mind. Agency manuals are on the list too.

The two dotted branches are the honest part. The corpus holds the guidance layer and the statute and CFR beneath it. What it does not hold is any adjudicated wage-and-hour outcome, which is a separate universe.

Status, withdrawal, and why currency is the hard part here

Opinion letters have been withdrawn and reissued across administrations. A batch of letters signed in January 2009 was withdrawn on March 2, 2009 "for further consideration," and on January 5, 2018 WHD reissued 17 letters under new numbers, for example FLSA2018-12, which says it reproduces the text of FLSA2009-31 verbatim (DOL, FLSA2018-12). DOL says the letters were stopped and replaced by general guidance in 2010, and it reinstated them on June 27, 2017 (DOL news release). In between, WHD put out Administrator Interpretations such as FLSA2010-1 and FLSA2010-2 (DOL, Administrator Interpretations).

A reissued pair shares a single PDF on dol.gov but is two documents with two numbers, two dates and opposite status, so each is served under its own act_id and the withdrawn predecessor stays retrievable rather than being overwritten by its replacement. That matters directly for a 29 U.S.C. 259 question, where the superseded text is often the one being relied on.

The useful part is that DOL publishes a withdrawal apparatus a machine can read, which most agencies in this corpus do not. actStatus on this source is read off DOL's own footnote table and disclaimer lines rather than inferred by us.

The live GET /us/statutes/coverage response reports a status breakdown for the whole federal AGENCY_GUIDANCE corpus: in force, non-precedential, superseded, rescinded, reserved, withdrawn, repealed and vacated. Vacated is the narrowest of those signals: a search for whd_opinion_letter with actStatus vacated returned a single letter on 12 October 2026.

Coverage, and how to read the numbers

The coverage endpoint is the authoritative counter. It is free to call and names every source in its AGENCY_GUIDANCE legend, so take any number you put in front of a customer from GET /us/statutes/coverage rather than from a page like this one.

Querying it

Base URL is https://api.vaquill.ai/api/v1. Auth is a bearer key with a vq_key_ prefix. Statutes routes are mounted under /us/statutes/*.

One opinion-letter query

curl -s https://api.vaquill.ai/api/v1/us/statutes/search \
  -H "Authorization: Bearer vq_key_..." \
  -H "Content-Type: application/json" \
  -d '{
    "query": "salary basis test for an exempt employee docked for a partial day absence",
    "corpusType": "AGENCY_GUIDANCE",
    "source": "whd_opinion_letter",
    "limit": 10
  }'

Both WHD sources at once, then split by source on the way out

curl -s https://api.vaquill.ai/api/v1/us/statutes/search \
  -H "Authorization: Bearer vq_key_..." \
  -H "Content-Type: application/json" \
  -d '{
    "query": "tip credit and tip pooling for a dual jobs employee",
    "corpusType": "AGENCY_GUIDANCE",
    "source": ["whd_opinion_letter", "whd_foh"],
    "matchType": "any",
    "limit": 20,
    "excerptChars": 600
  }'

Each hit carries a stable actId and the publisher's own dol.gov URL in externalUrl. Take the actId from the response and fetch the document with GET /us/statutes/section/{actId} or /section/{actId}/body.

Not run as written in our October 2026 review, because the endpoint needs an API key. We ran the same two queries through the Vaquill MCP server on 12 October 2026. The first returned WHD_OL_FLSA_FLSA2018_14 (issued 2018-01-05, actStatus in_force) and WHD_OL_FLSA_FLSA2005_46. The second returned FOH_S30d06 (source whd_foh, goodLawStatus unknown), FOH_S32j18 and WHD_OL_FLSA_FLSA2026_13, each with a dol.gov externalUrl.

Filters that matter for this corpus

Citation forms to render

Get these right or the output will not survive review.

• Opinion letter: WHD Opinion Letter FLSA2020-13
• Field Operations Handbook: FOH 31c05

The letter prefix encodes the statute (FLSA, FMLA, and so on), which is load-bearing. Dropping it makes the cite unresolvable, because the year-and-number portion repeats across the series.

What is not in these two sources

State this to your users before they find it out.

• Adjudicated outcomes. Neither source is a decision. Both are the guidance layer.
• State wage-and-hour law. State minimum wage, overtime and wage-payment rules live in the state statutes and state regulations corpora, which is a different query.
• A safe-harbor determination. The API serves the document and its provenance. Whether 29 U.S.C. 259 is available on a given set of facts is a legal conclusion the data does not contain.
• Unpublished or informal WHD correspondence. Only what WHD publishes is served.

Because status here can change without the text changing, this is a corpus where change detection is worth wiring in rather than caching once and moving on. GET /boards is free and reports which corpora are watchable, with a cadence and a lastRetrievedAt. Federal agency guidance is one board, and on 12 October 2026 it listed a monthly cadence and whd_opinion_letter among its scopable sources. The Field Operations Handbook (whd_foh) sits on the separate agency manuals board.

FAQ

What is a DOL Wage and Hour opinion letter?

It is the Wage and Hour Division's written answer to a specific factual question put to it by a named requester, stating how the Division reads the FLSA, FMLA, SCA, DBRA, CCPA or MSPA on those facts. It binds the agency's own enforcement posture rather than a court. It is not a statute and not a regulation, and it was issued without notice-and-comment rulemaking.

Is an opinion letter binding law?

No. The binding text is the statute at 29 U.S.C. 201 and following and the regulations at 29 C.F.R. An opinion letter is sub-regulatory guidance that tells you how the Division reads those instruments, which is a statement about enforcement risk rather than a holding you can cite as controlling authority.

Why do opinion letters matter more than most agency guidance?

Because of 29 U.S.C. 259, section 10 of the Portal-to-Portal Act. An employer that pleads and proves it acted in good faith in conformity with and in reliance on a written ruling or interpretation of the Wage and Hour Administrator has a bar to an FLSA minimum wage or overtime claim, and the statute preserves that defense even where the interpretation is later modified, rescinded or held invalid. That makes the document legally operative in a way a general policy memo is not, though DOL says the Portal-to-Portal Act does not, with exceptions, reach the FMLA or the other statutes WHD enforces.

What is the Field Operations Handbook, and can I cite it?

The FOH is WHD's internal manual for its own investigators, covering how an investigation is run and how the rules are applied in the field. WHD's own pages say the material may not reflect current legislation, regulations or court decisions and that the Federal Register and the CFR remain the official resources. Treat it as evidence of agency procedure and interpretation, not as authority.

Does the API tell me whether an opinion letter has been withdrawn?

Yes, and unusually so for this corpus family. actStatus for whd_opinion_letter is read off DOL's own footnote table and disclaimer lines rather than inferred, and it distinguishes in force, withdrawn, superseded and vacated. Withdrawn predecessors stay retrievable under their own act_id rather than being overwritten by a reissued replacement, which matters when the superseded text is the one someone relied on.

How do I filter to just the WHD sources?

Set corpusType to AGENCY_GUIDANCE and source to whd_opinion_letter, whd_foh, or both as a list. Both codes appear in the source enum of the public spec at https://api.vaquill.ai/external/openapi.json, and an unrecognized value is rejected with a 422 rather than silently matching nothing.

How many WHD documents are in the corpus?

The published per-source table records 594 opinion, ruling and Administrator Interpretation letters covering 1993 to 2026, and 1,500 Field Operations Handbook provisions covering 1966 to 2025, measured 2026-09-07. For a current figure, take GET /us/statutes/coverage as the authoritative counter.

Can I retrieve how a letter read on a past date?

Yes, as a reconstruction. Add asOf=YYYY-MM-DD to the section body call and the earlier text is rebuilt from observed changes, with isBounded set when the answer depends on when change capture began. No stored published edition exists for WHD, the coverage notes make no boundedness claim for either WHD source, and a date before capture began can come back unavailable. For a reliance question, the defensible artifact is the publisher's own copy at the dol.gov URL carried on every record.

Where does the text come from?

From DOL's own publication pages, not a commercial aggregator, and every record carries the publisher's URL so a reviewer can check the original.

Where to go next

The two WHD sources are 2 of the 53 named sources under corpusType=AGENCY_GUIDANCE. The federal agency guidance overview covers the rest of the token and how the source filter partitions it, and the API overview covers auth, the statutes routes, and what the rest of the US corpus holds.

Priyansh Khodiyar

Co-Founder & CTO

Priyansh leads engineering and AI at Vaquill AI: the pipelines that pull statutes, regulations and court rules from every US jurisdiction's official publisher, and the REST API, MCP server and open dataset that serve them.