45 U.S.C. § 231h
Employers shall file with the Board, in such manner and form and at such times as the Board by rules and regulations may prescribe, returns of compensation of employees, and, if the Board shall so require, shall furnish employees with statements of their compensation as reported to the Board. The Board's record of the compensation so returned shall be conclusive as to the amount of compensation paid to an employee during each period covered by the return, and the fact that the Board's records show that no return was made of the compensation claimed to have been paid to an employee during a particular period shall be taken as conclusive that no compensation was paid to such employee during that period, unless the error in the amount of compensation returned in the one case, or the failure to make return of the compensation in the other case, is called to the attention of the Board within four years after the day on which return of the compensation was required to be made.
45 U.S.C. § 231h