Automatic Data Processing Inc. plans to complain to regulators about what it claims are “false and misleading statements” made by Bill Ackman, as the proxy fight at the payroll and human resources outsourcer escalates ahead of a shareholder vote.

ADP said Tuesday it will file a complaint with the U.S. Securities and Exchange Commission over an 18-page letter billionaire activist investor Ackman sent to Institutional Shareholder Services Inc. In Monday’s letter, Ackman claimed ADP had provided “non-public, inaccurate and misleading statements” of its own to the proxy advisory firm.

“Mr. Ackman’s reckless and unfounded assertions continue to undermine his credibility and are inconsistent with the temperament of a reputable board member,” ADP said in a statement.

A representative for Ackman’s Pershing Square Capital Management wasn’t immediately able to comment on the letter.

The war of words comes ahead of an annual meeting Nov. 7, where ADP shareholders will vote on whether to support Ackman’s three candidates for the board or keep ADP’s slate of 10 directors. Pershing Square disclosed an 8.3 percent stake in ADP in stocks and options in August.

Ackman has won the backing of two shareholder advisory firms -- Glass Lewis & Co. and Egan-Jones Proxy Services. ISS has recommended shareholders withhold support for one of management’s nominees, Eric Fast, in order to make room for Ackman on the board.

In his letter to ISS, Ackman said he believed ADP had tried to “mislead” the firm by making private statements about matters that it’s refused to address publicly during the proxy fight. He claimed those comments revolved around a new product offering, labor productivity and its margins and targets.

ADP hasn’t disclosed any material non-public information in its meetings with ISS or any other party, the company said Tuesday. It did acknowledge a chart related to its margin targets in an Oct. 17 presentation was mislabeled and has been fixed.

“Mr. Ackman is distorting the facts, misleading shareholders and seeking to discredit ADP to win votes in the final days of this proxy contest,” it said.

This article was provided by Bloomberg News.