An employee who elects CSRS coverage under Sec. 847.411 is prospectively subject to both the Old Age, Survivors, and Disability Insurance (OASDI) tax and CSRS as described in subpart J of part 831 of this chapter, known as CSRS Offset, effective from the first day of the next pay period after the employing agency receives the employee's election under Sec. 847.411(a).