20 C.F.R. § 345.120 – Assessment and collection of contributions or underpayments of contributions.

(a) If any employer's contribution is not paid to the Board when due or is not paid in full when due, the Board may, as the circumstances warrant, assess the contribution or the deficiency and any interest or penalty applicable under this part (whether or not the deficiency is adjustable as an underpayment under § 345.118 of this part).
(b) The amount of any such assessment will be collected in accordance with the applicable provisions of law. If any employer liable to pay any contribution neglects or refuses to pay the same within ten days after notice and demand, the Board may collect such contribution with such interest and other additional amounts as are required by law, by levy, by administrative offset as authorized by 31 U.S.C. 3716 and in accordance with the procedures set forth in part 367 of this chapter, or by a proceeding in court, but only if the levy is made or proceeding begun:
1. (1) Within 10 years after assessment of the contribution; or
2. (2) Prior to the expiration of any period, including extension thereof, for collection agreed upon by the Chief Financial Officer and the employer.
(c) All provisions of law, including penalties, applicable with respect to any tax imposed by the provisions of the Railroad Retirement Tax Act and the regulations thereunder, insofar as not inconsistent with the provisions in this part, shall be applicable with respect to the assessment and collection of contributions under this part.