20 C.F.R. § 216.22
Work as an employee which affects payment
(a) Work for a railroad employer. Work for pay as an employee of a railroad employer always prevents payment of an annuity.
(b) Work for last non-railroad employer. Work for pay in the service of the last non-railroad employer by whom an individual is employed will reduce the amount of the tier II benefit of the employee, spouse and supplemental annuity as provided in part 230 of this chapter. An individual's last non-railroad employer is:
(1) Any non-railroad employer from whom the individual last resigned (in point of time) in order to receive an annuity; and
(2) Any additional non-railroad employer from whom the individual resigned in order to have an annuity become payable. Employment which an individual stops within 6 months of the date on which the individual files for an annuity will be presumed in the absence of evidence to the contrary to be service from which the individual resigned in order to receive an annuity.
(c) Corporate officers. An officer of a corporation will be considered to be an employee of the corporation. A director of a corporation acting solely in his or her capacity as such director is not an employee of the corporation.