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 turns a written WHD interpretation into a defense an employer can plead.

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 ruling or interpretation of the Administrator of the Wage and Hour Division has a defense to FLSA liability, and the statute preserves that defense even where the interpretation is later modified or rescinded.
• 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: 34 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 enum in the deployed spec at https://api.vaquill.ai/external/openapi.json, which is public and needs no key. The enum carries 77 values in total, and an unrecognized one is rejected with a 422 whose body lists every valid code, so a single bad request returns the whole vocabulary.

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, gives an employer a defense to FLSA liability where the act complained of was in good faith in conformity with and in reliance on a 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. The statute preserves the defense even if the ruling or interpretation is afterwards modified, rescinded, or held invalid.

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 only serves current text is the wrong shape for this question.

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 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. The corpus carries that as goodLawStatus: unknown rather than defaulting the source to in force.

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. There was a mass withdrawal on March 2, 2009, and 17 of those letters were reissued in 2018 under new numbers. Between 2010 and 2017 WHD stopped issuing opinion letters altogether and published Administrator Interpretations instead, which are the only documents covering that period.

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 of 40,216 in force, 35,485 non-precedential, 5,305 superseded, 283 rescinded, 112 reserved, 33 withdrawn, 15 repealed and 2 vacated, measured 2026-09-07. The two vacated documents in that whole corpus are the two opinion letters the Administrative Review Board vacated, which is a useful sense of how small and specific a signal this is.

Coverage, and how to read the numbers

On the opinion letters specifically, the publisher's index lists 596 records and 594 are served. The two that are not, FLSA2009-1NA and FLSA2009-2NA, carry a truncated PDF path with no filename that 404s on dol.gov itself, so they are recorded as fetch failures rather than invented. The numbering is otherwise intact.

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. Take the actId from the response and fetch the document with GET /us/statutes/section/{actId} or /section/{actId}/body.

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 sources are watchable, with a cadence, a lastRetrievedAt and a retrievalStatus.

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 defense to FLSA liability, and the statute preserves that defense even where the interpretation is later modified or rescinded. That makes the document legally operative in a way a general policy memo is not.

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 returns 422 with the full list of valid codes 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 2026-09-06. That table carries its own warning that its rows sum higher than the endpoint reports for the token, so read each row as an upper bound and take GET /us/statutes/coverage as the authoritative counter.

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

Not as a stored published edition. asOf=YYYY-MM-DD reconstructs earlier text from observed changes and sets isBounded when the answer depends on when change capture began, and the coverage notes make no boundedness claim for either WHD source. 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 a document could not be fetched it is recorded as a fetch failure rather than filled in from elsewhere, which is why two letters on WHD's index of 596 are declared missing instead of quietly reconstructed.

Where to go next

The two WHD sources are 2 of the 51 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, from the matter workbench to drafting, document comparison, document matrix, and citation-verified research.