Rehire Vesting Service

Can a governmental 401(a) DC plan require rehired eligible employees, who were 100% vested at termination, to repay their entire distribution in order to have vesting service restored? The rehire would need to repay the distribution the earlier of 5 years after their rehire date or 5 years after the distribution was paid. If paid within this period the rehire will be 100% vested. (Yes, they want the 5-year period to begin after the distribution date and not the termination date.)

Thank you.