Upon the vesting of nonqualified deferred compensation (NQDC), which includes RSUs that have a share-deferral feature, Social Security and Medicare taxes (FICA) are owed. Under the nonduplication rule, once deferred compensation is subject to FICA taxes, they are not owed again when the shares are distributed. If companies do not withhold FICA taxes correctly at vesting, the plan participant will need to pay FICA taxes on the value of the shares at the time of share delivery.

For more details on this FICA tax timing rule, see an article from the law firm Foley & Lardner. A commentary from the law firm Spencer Fane looks at some of the complications that can arise when the special timing rule is not followed and explains new restrictions on how companies can correct a mistake in FICA taxation.