BOSTON (Reuters) - Billionaire investor William Ackman on Monday accused Automatic Data Processing Inc ADP.O of providing misleading and incorrect claims to Institutional Shareholder Services and asked the proxy advisory firm to reconsider its shareholder recommendations.

William 'Bill' Ackman, CEO and Portfolio Manager of Pershing Square Capital Management, speaks during the Sohn Investment Conference in New York City, U.S., May 8, 2017. REUTERS/Brendan McDermid

ISS on Wednesday issued a report to guide institutional investors in a vote next week where the hedge fund manager hopes to win three ADP board seats. The proxy adviser recommended shareholders largely vote for the company’s slate but supported Ackman’s election.

Ackman’s filing, an usual criticism of a proxy adviser by an activist, came hours after the human resources outsourcing company’s board chair John Jones said in a letter to shareholders that ADP is not underperforming and plans to improve margins and profit further.

“ADP provided non-public, inaccurate and misleading information, claims, and arguments which were relied upon by ISS,” Ackman said in a regulatory filing made with the U.S. Securities and Exchange Commission.

ADP and ISS had no immediate comment on Monday.

Ackman’s unveiled his stake of 8.3 percent, including 2 percent in common shares, in ADP in August, and has since criticized the company for what he calls sluggish earnings and inefficient operations. He plans to hold another investor webinar on Nov. 1.

“ISS accepted, and in its Report has publicly endorsed, certain misleading or incorrect factual assertions made by ADP management during its engagement with ISS,” Ackman said in the filing.

ISS said in its recommendation that shareholders should withhold their vote for ADP director Eric Fast to make room for Ackman but that the case was not “sufficiently compelling to justify replacing three directors.”

Glass Lewis and Egan-Jones last week both recommended all of Ackman’s directors.

Ackman took aim at the projection provided by ADP’s board chair on Wednesday, in which he said the company plans to improve its operating margin by 500 basis points between 2017 and 2020 and speed up its profit growth.

“This is a new and inaccurate disclosure that we believe is demonstrably false, and is intended to mislead shareholders and others about the lack of progress implied by ADP’s plan,” Ackman said in the filing.

Ackman also said that ISS failed to follow its own guidelines stating that it relies only on publicly disclosed information to reach its recommendations.

He flagged ADP’s labor productivity figures and the reference to an “upcoming release” of the Vantage 2.0 platform in the ISS report.

“The disclosure that ADP is close to releasing a Vantage 2.0 product offering for the Enterprise segment is material, even more so in the context of this proxy contest,” he said.