If the method in paragraph (b)(1) of this section is used, the taxpayer may change to the method in paragraph (b)(2) of this section without obtaining permission from the Internal Revenue Service. However, once the election to use the method in paragraph (b)(2) of this section is made, the taxpayer may not change the method of reporting without permission from the Internal Revenue Service. For further information on Federal income taxes, the Service Center Director or District Director, Internal Revenue Service, of the taxpayer's district should be contacted.
31 C.F.R. § 342.6