Every employee of the state, including public school employees as defined under section 2 (c) of this act, whose services are covered by an agreement entered into under section 3 shall be required to pay for the period of such coverage, into the contribution fund established by section 13, at such time or times as the secretary of health, education, and welfare may by regulation prescribe, amounts equivalent to the sum of the taxes which would be imposed under the federal insurance contributions act if the services of employees covered by this agreement constituted employment as defined in such act.