Every state employee whose services are covered by an agreement entered into under section 88-212 shall be required to pay for the period of the coverage, into the contribution fund established by section 88-224, contributions, with respect to wages (as defined in § 88-211 ) equal to the amount of the employee tax which would be imposed by the Federal Insurance Contributions Act if the services constituted employment within the meaning of that Act. Such liability shall arise in consideration of the employee’s retention in the service of the State, or the employee’s entry upon such service, after June 10, 1953.