(7) A corporation is an affiliate of an employer if it is a member of any controlled group of corporations (as defined in section 1563(a) of title 26 , except that “applicable percentage” shall be substituted for “80 percent” wherever the latter percentage appears in such section) of which the employer who maintains the plan is a member. For purposes of the preceding sentence, the term “applicable percentage” means 50 percent, or such lower percentage as the Secretary may prescribe by regulation. A person other than a corporation shall be treated as an affiliate of an employer to the extent provided in regulations of the Secretary. An employer which is a person other than a corporation shall be treated as affiliated with another person to the extent provided by regulations of the Secretary. Regulations under this paragraph shall be prescribed only after consultation and coordination with the Secretary of the Treasury.