On June 12, Yahoo said it would run advertisements supplied by Google alongside search query results, a four-year deal estimated to bring Yahoo up to $800 million in revenue a year.
"We are continuing to have cooperative discussions with the Department of Justice about this arrangement," Google said in a statement. "We are confident that the arrangement is beneficial to competition, but we are not going to discuss the details of the process."
Yahoo did not have a comment.
The deal with Google, which already dominates text-based search advertising, was widely characterized as a move by Yahoo to deflect Microsoft's acquisition attempts.
In April, Yahoo and Google informed the DOJ of a planned two-week test of the advertising program, which was limited to U.S. traffic on yahoo.com and comprised no more than 3 percent of total search queries.
After reaching a larger agreement last month, the two companies said they would delay implementing the program for three and a half months pending a voluntary review by the DOJ, the Post reported. But the newspaper characterized the DOJ as now undertaking a formal investigation of the deal.