Considering the nature of the industry, it's likely that both the holding companies and their individual agencies are being named.
In a statement, holding company Interpublic Group of Cos. said, "Diversity and inclusion will continue to be a significant priority for IPG. Our industry-leading [diversity and inclusion] programs are resulting in progress against this important business goal and we remain open to further dialogue with Mr. Mehri, though we are unaware of any developments relating to the EEOC."
Representatives from holding companies WPP, Publicis Groupe and Omnicom Group did not respond before deadline.
Meanwhile, Mr. Mehri is free to continue building his class-action suit, regardless of the outcome of the federal agency's inquiry, which could take months if not longer.
This development comes more than one year after Mr. Mehri and the NAACP announced the Madison Avenue Project, a report to lay the foundation for a class-action suit against the ad industry. The report found that ad agencies are guilty of "pervasive racial discrimination," including black employees earning only 80% of the salaries of comparable white employees.
Since then, Mr. Mehri and his firm, Mehri & Skalet, have been investigating claims of race discrimination and interviewing potential plaintiffs.
"From my point of view, things are going at a good pace," he said. "It's a long road that has to happen person by person, piece by piece. The wheels are moving in the direction of something happening."
At this point, Mr. Mehri sees two potential outcomes: a class-action suit or settlements between the agencies and individuals. But that will take time.
To compare, Mr. Mehri's "Women on Wall Street" gender discrimination case against financial institutions took more than two years between the EEOC filing and the eventual settlement. Mehri & Skalet specializes in class-action cases -- among the most notable was a suit against Texaco. In that 1990s case, a Texaco exec was famously caught on tape saying, "All the black jelly beans seem to be glued to the bottom of the bag."
For the Madison Avenue Project, some industry vets worry that finding a similar "big smoking gun" will be tricky.
"It's a very difficult thing to do, because bias is hard to prove," said Hadji Williams, blogger and author of "Knock the Hustle." "[The ad industry] is an at-will industry. It doesn't have unions or hiring codes or contract bidding processes that they have to adhere by."
"Everybody knows there are biases, but until you find a memo about a standard practice or someone on tape higher-up at an agency, it will be hard to prove," he said.