For a DB plan with mandatory employee contributions, USERRA permits an employer to require the contributions to be made up before crediting service. It also requires that the employee be permitted to contribute makeup contributions during the period starting with the date of reemployment and continuing for up to three times the length of the employee's immediate past period of uniformed service, not to exceed five years.

Is anyone aware of any guidance on whether this period is tolled if an employee is redeployed while making up payments for a previous period of qualified military service? Seems to me that it should be, but I haven't seen anything on it.

As it turns out, I just came across the answer to this: The period for making up missed contributions is NOT required to be tolled on account of a second period of military service (though an employer is permitted to voluntarily extend it). This is in the preamble to the final regs - 70 Fed Reg 75246, on pages 75281-75282.