The following rules apply in determining the number and size of employers, as required by the MSP provisions for the aged and disabled:

(a) All employers that are treated as a single employer under subsection (a) or (b) of section 52 of the Internal Revenue Code (IRC) of 1986 (26 U.S.C. 52 (a) and (b)) are treated as a single employer.

(b) All employees of the members of an affiliated service group (as defined in section 414(m) of the IRC (26 U.S.C. 414m)) are treated as employed by a single employer.

(c) Leased employees (as defined in section 414(n)(2) of the IRC (26 U.S.C. 414(n)(2)) are treated as employees of the person for whom they perform services to the same extent as they are treated under section 414(n) of the IRC.

(d) In applying the IRC provisions identified in this section, CMS relies upon regulations and decisions of the Secretary of the Treasury respecting those provisions.