29 CFR § 99.220 - Frequency of audits.
Except for the provisions for biennial audits provided in paragraphs (a) and (b) of this section, audits required by this part shall be performed annually. Any biennial audit shall cover both years within the biennial period.
(a) A State or local government that is required by constitution or statute, in effect on January 1, 1987, to undergo its audits less frequently than annually, is permitted to undergo its audits pursuant to this part biennially. This requirement must still be in effect for the biennial period under audit.
(b) Any non-profit organization that had biennial audits for all biennial periods ending between July 1, 1992, and January 1, 1995, is permitted to undergo its audits pursuant to this part biennially.