This excerpt taken from the AKS 8-K filed Oct 22, 2008.
Share Withholding. With respect to withholding required upon the exercise of Options, the vesting of Shares under a Restricted Stock Award, or receipt of Shares pursuant to a Performance Share Award, Participants may elect, subject to the approval of the Committee, to satisfy the withholding requirement, in whole or in part, by having the Company withhold Shares having a Fair Market Value on the date the tax is to be determined equal to the minimum statutory total tax which could be imposed on the transaction. All elections shall be irrevocable, made in writing, signed by the Participant. In addition to the foregoing requirements, an Insider may elect Share withholding only if such election is made in compliance with Section 16 of the Exchange Act.