Effective July 1, 2000, and subject to the rules adopted by the board of trustees, the system shall accept an eligible rollover distribution or a direct transfer of funds from another eligible retirement plan, as defined under applicable federal law, or an individual retirement account, in payment of all or a portion of the cost to purchase optional service credit or to reinstate previously withdrawn service credit as permitted by the system. The system may only accept rollover payments in an amount equal to or less than the balance due for purchase or reinstatement of service credit. The rules adopted by the board of trustees shall condition the acceptance of a rollover or transfer from another eligible retirement plan or an individual retirement account on the receipt of information necessary to enable the system to determine the eligibility of any transferred funds for tax-free rollover treatment or other treatment under federal income tax law.