42 CFR §408.44

1. (a)Responsibility for deductions. If an enrollee is not entitled to railroad retirement benefits or social security benefits, and is receiving a civil service annuity, the premiums are deducted from that annuity by the Office of Personnel Management (OPM) on the basis of a notice from SSA indicating that the annuitant is entitled to SMI.
2. (b)Deduction of spouse's premiums. If the annuitant's spouse is also enrolled for SMI and is not entitled to a civil service annuity or to social security or railroad retirement benefits, and the annuitant gives written consent, OPM also deducts the spouse's premium from the annuitant's monthly check.
3. (c)Withdrawal of annuitant's consent.
   1. (1)If an annuitant wishes to withdraw consent for deduction of the spouse's premium, he or she must send written notice of withdrawal to OPM.
   2. (2)The withdrawal notice is effective with the third month after the month in which it is received, or with the month specified in the notice, whichever is later.