Bill Ackman's Pershing Square Capital Management disclosed an 8.3% stake in ADP.

Pershing said it has engaged in and intends to continue to engage in discussions with the company's management and board, other stockholders and other interested parties that may relate to the governance and board composition, business, operations, cost structure, management, assets, capitalization, financial condition, strategic plans, and the future of ADP. Initial discussions with the company to extend its August 10 director nominations deadline have not resulted in an extension. Pershing wrote in a regulatory filing which allows for activism.

As a result Pershing is submitting a stockholder proposal and director nomination notice to ADP. The fund earlier announced in a press release the nomination of three board members, one of which is Bill Ackman.