All employees of the Commonwealth and its agencies commencing employment or who are reemployed on or after January 1, 2008, in a position covered by the Virginia Retirement System, and who (i) have not elected to participate in a plan established pursuant to § 403(b) of the Internal Revenue Code of 1986, as amended, or (ii) do not participate in the hybrid retirement program described in § 51.1-169, shall participate in the plan described in § 51.1-602, unless such employee elects, in a manner prescribed by the Board, not to participate in such plan. The amount of the deferral for any such employee participating in the plan shall equal, on a semimonthly basis, $20 of otherwise payable compensation, unless the employee elects to defer a different amount.