This excerpt taken from the C 10-K filed Feb 23, 2007.
(2) Senior Executive Obligations and Restrictions.
As a Senior Executive, you are subject to the Citigroup Stock Ownership Commitment (SOC) under which you must agree to hold 75% of any Citigroup stock you own today or acquire from the company in the future. Additional information about the SOC will be provided to you under separate cover. Also, you shall be subject to certain Sarbanes-Oxley company-related loan restrictions.