A U.S. Justice Department investigation into suspected manipulation of the bidding process for production work has concluded for several holding companies.

Omnicom Group, MDC Partners and Publicis Group all confirmed the probes have closed without any action being taken against them in separate Securities and Exchange Commission (SEC) filings published today. IPG confirmed via email. As did WPP, which had three of its subsidiaries subpoenaed by the U.S. Department of Justice Antitrust Division.

In 2016, the Wall Street Journal reported Ad agencies may have been funneling work to their in-house production units by pressuring independent production companies to bow out of contract bids.

A number of production companies claimed they had received requests from ad agencies to inflate their bids for commercial work, making them seem less attractive to clients. In comparison, the uninflated bids from agency production companies or shops within the same holding company appeared more reasonable.

This story first appeared on campaignlive.com.