Activist investor Pershing Square Capital Management LP said on Monday the chief executive of Automatic Data Processing Inc had "unfairly characterized" their interactions in an effort to make the hedge fund's requests "appear unreasonable."

ADP had earlier this month said Ackman wanted effective control of the company through five board seats and a CEO change.

Pershing, led by billionaire investor William Ackman, said on Monday it had not sought effective control of ADP at any time and had expressed an openness to work with CEO Carlos Rodriguez.

According to a filing on Monday, Pershing said Rodriguez had mistakenly sent an email to Ackman instead of ADP's general counsel on Aug. 6.

In the mail, Rodriguez said he did not find Ackman's willingness to work with him to be credible as it was conditioned on him having the same view. The hedge fund had proposed three nominees to ADP's board last week, setting the stage for a proxy contest with the human resources outsourcing company.