26 C.F.R. § 301.7516-1
The Commissioner is authorized, within his discretion, upon written request, to admit employees and officials of any State, the Commonwealth of Puerto Rico, any possession of the United States, any political subdivision or instrumentality of any of the foregoing, the District of Columbia, or any foreign government to training courses conducted by the Internal Revenue Service, and to supply them with texts and other training aids. Requests for such training or training aids should be addressed to the Commissioner of Internal Revenue, Washington, D.C. 20224, Attention: A: T, except that requests involving officials or visitors of foreign governments should be addressed to the Commissioner of Internal Revenue, Washington, D.C. 20224. Attention: C: FA. The Commissioner may require payment from the party or parties making the request of a reasonable fee not to exceed the cost of the training and training aids supplied pursuant to such request.
26 C.F.R. §301.7516-1