Omnicom Group's (OMC) proposed merger with fellow advertising company Interpublic Group (IPG) is facing a probe over the companies' potential connection with an anti-conservative cartel that sought to defund news outlets, the New York Post reported Wednesday.

As part of an antitrust probe, House Judiciary Committee Chairman Jim Jordan sent letters to the respective chief executives of both companies, which were founding members of the World Federation of Advertisers and its now-defunct Global Alliance for Responsible Media initiative, according to the report.

Omnicom and Interpublic have been ordered to preserve documents and all contact with the World Federation of Advertisers and the Global Alliance for Responsible Media, and give information to the House, the news outlet reported, citing letters obtained by it.

The committee is seeking answers from the companies no later than the afternoon of Jan. 7, according to the report.

Omnicom and Interpublic didn't immediately respond to MT Newswires and the Post's separate requests for comment.

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