Congresswoman Norton (representing Washington DC) introduced a bill before Congress that would provide for compensation of Federal contractor employees that may be placed on unpaid leave as a result of any Federal Government shutdown. She calls it the "Low-Wage Federal Contractor Employee Back Pay Act of 2018".
Under this proposed legislation, if a Federal contractor that provides retail, food, custodial, or security services for the Federal Government places employees on unpaid leave as a result of any lapse in appropriations which begins in Fiscal Year 2018, the Government shall provide compensation to those employees at their standard rate of compensation for the period of such lapse.
The proposed legislation is not any more specific with respect to which contracts and/or which contractor employees are covered. The language presented is very generic and implementation will be open to interpretation (or through regulation).
Its like getting additional paid vacation.