20 C.F.R. § 204.1
In order for an individual to receive credit under the Railroad Retirement Act (Act) for railroad service prior to 1937, he or she must establish that he or she was actively working for an employer under the Act on August 29, 1935, or was in an employment relation to an emp]oyer on that date. Section 204.3 of this part defines employment relation for purposes of establishing prior service. It is also necessary to establish an employment relation to an employer for any month in which an individual wishes to receive a deemed service month, as provided for in § 210.3 of this chapter, and to receive credit for pay for time lost as provided for in § 211.3 of this chapter. This part defines employment relation for these purposes. See §§ 204.5 and 204.6 . In addition, in order for an individual to have his or her service to a local lodge or division of a railway labor organization considered as creditable service under the Act, he or she must establish that he or she was working for a railroad or in an employment relation to a railroad on or after August 29, 1935, and that such employment or employment relation preceded his or her service to the local lodge or division. Section 204.7 defines employment relation for this purpose.
20 C.F.R. §204.1