Is a private letter ruling binding precedent?

No. A private letter ruling binds the IRS only as to the taxpayer who requested it, and Section 6110(k)(3) says it may not be used or cited as precedent by anyone else. PLRs are still read as evidence of the IRS's thinking, and they count — at reduced weight — toward substantial authority under the penalty regulations. But a position built primarily on someone else's PLR is built on sand.

Do Treasury regulations have the force of law?

Generally yes, when validly issued. Treasury regulations interpret the statute and bind both the IRS and taxpayers unless a court holds them invalid — a possibility that became more live after the Supreme Court ended Chevron deference in 2024. Sub-regulatory guidance such as revenue procedures and notices binds IRS personnel but has less weight in court.

What outranks what: the hierarchy of tax authority

The rules of tax come in ranked layers. The Internal Revenue Code — the statute, readable at uscode.house.gov — outranks everything. Treasury regulations, published at eCFR Title 26, interpret the statute and generally carry the force of law. Below them sits sub-regulatory guidance — revenue rulings, revenue procedures, notices — which binds IRS personnel but gets less respect in court. Court decisions interpret all of it, and a private letter ruling binds no one but the taxpayer who bought it.

Knowing the ranking is not academic. Penalty defenses, audit outcomes, and the honest answer to "can we take this position?" all turn on which rung your support sits on.

The rungs, top to bottom

A working ranking, from binding law to persuasive scraps:

Rung	Examples	Who it binds
Statute	IRC §41, §174A	Everyone
Treaties	Bilateral tax treaties	Everyone (co-equal with statute; later-in-time controls)
Regulations	Treas. Reg. §1.41-4	IRS and taxpayers, unless invalidated
Published IRS guidance	Revenue rulings, revenue procedures, notices	IRS personnel; taxpayers may rely
Case law	Tax Court, district courts, circuit courts	Parties; precedent within the jurisdiction
Private and internal guidance	PLRs, TAMs, CCAs, audit techniques guides	The recipient (PLR/TAM) or no one
Legislative history, articles, treatises	Committee reports, commentary	No one; persuasive only

Case law's rank is slippery: a Supreme Court holding outranks a regulation, while a single Tax Court memorandum opinion may not. And since the Supreme Court discarded Chevron deference in 2024, regulations are more contestable than the table suggests — courts now interpret ambiguous statutes themselves rather than deferring to Treasury's reading.

How "substantial authority" weighs the rungs

The hierarchy is operationalized in the accuracy-penalty rules. Treas. Reg. §1.6662-4(d) lists what counts as "authority" — statutes, regulations, published guidance, cases, committee reports, even PLRs and TAMs — and instructs that weight depends on both the source's rank and its relevance to your facts. A squarely on-point revenue ruling can outweigh an off-point case; a general counsel memorandum "has little weight." Notably absent from the list: treatises, articles, and anything a provider's marketing deck says. If your penalty defense rests on a source the regulation does not recognize, it rests on nothing.

Why a PLR is not precedent

A private letter ruling is the IRS's written answer to one taxpayer's question about one set of facts, issued for a user fee. Section 6110 makes rulings publicly readable but 6110(k)(3) forbids their use as precedent. The IRS can — and does — take the opposite position against the next taxpayer. PLRs are best read as weather reports: useful evidence of current agency thinking, meaningless as law. The same is true of the audit techniques guides examiners use in specialty-tax exams: instructive about what the IRS will probe, binding on nobody.