IRS Form 3922
Corporations are required to file Form 3922 with the IRS for each transfer of the legal title of a share of stock acquired by an employee pursuant to that employee's exercise of an option granted under an employee stock purchase plan and described in section 423(c) of the IRC (where the exercise price is less than 100% of the value of the stock on the date of grant, or is not fixed or determinable on the date of grant).
IRS Form 3922 - available here
Who Must File Form 3922
Every corporation, which in any calendar year records, or has by its agent recorded, a transfer of the legal title of a share of stock acquired by the transferor (person who acquires the shares pursuant to the exercise of the option) pursuant to the transferor's exercise of an option granted under an employee stock purchase plan and described in section 423(c) (where the exercise price is less than 100% of the value of the stock on the date of grant, or is not fixed or determinable on the date of grant), must, for that calendar year, file Form 3922 for each transfer made during that year.
A return is required by reason of a transfer described in section 6039(a)(2) only for the first transfer of legal title of the shares by the transferor, including the first transfer of legal title to a recognized broker or financial institution. If a contractual agreement exists or is entered into with a recognized broker or financial institution pursuant to which shares acquired upon exercise of the option will be immediately deposited into a brokerage account established on behalf of the transferor, then the deposit of shares by the transferor into the brokerage account following the exercise of the option is the first transfer of legal title of the shares acquired by the transferor, and the corporation is only required to file a return relating to that transfer of legal title.
Shares of stock transferred as a result of the exercise of an option described above must be identified in a manner sufficient to enable the accurate reporting of the transfer of legal title to such shares. This identification can be made by assigning to the share certificates of stock issued pursuant to such options a special serial number or color.
The corporation whose stock is being transferred must file Form 3922.
Exception: A Form 3922 is not required for the first transfer of legal title of a share of stock by an employee who is a nonresident alien (as defined in section 7701(b)) and to whom the corporation is not required to provide a Form W-2, Wage and Tax Statement, for any calendar year within the time period beginning with the first day of the calendar year in which the option was granted to the employee and ending on the last day of the calendar year in which the employee first transferred legal title to shares acquired under the option.
For more information, please review IRS Instructions for Forms 3921 and 3922