Technical Advice Memorandums (TAMs) are requested by IRS area offices after a return has been filed, often in conjunction with an ongoing examination. They are similar to private letter rulings, but whereas letter rulings come from a taxpayer's request for advice on a proposed transaction, TAMs arise from IRS employees' requests for advice regarding the examination of a tax return.
"[A] technical advice memorandum to an area director, which relates to a particular case, should not be applied or relied upon as a precedent in the disposition of other cases. However, they provide insight with regard to the Service’s position on the law and serve as a guide" (IRM 184.108.40.206.10).
TAMs issued after October 31, 1976 may be used as substantial authority to avoid the substantial understatement penalty.
TAMs share the same multiple digit file numbers with letter rulings, i.e. the first two digits indicating the year the TAM/Ruling was issued, the second two digits indicating the week of the year the TAM/Ruling was released, and the remaining numbers indicating the number of the item issued that particular week (e.g. T.A.M. 99-32-001 or P.L.R. 99-32-083). TAMs carry the first release numbers for any particular week.
Lexis Advance and Westlaw carry TAMs from 1954 - present.