In a message to shareholders disclosed to the SEC, Bcom3 Chairman-CEO Roger Haupt said though the SEC's review is nearing an end, it is held up by a technical difference between French and U.S. accounting regulations.
"Our goal is to have the prospectus in your hands in August and a vote in September, but we obviously can't control the response rate of the SEC," Mr. Haupt's message said.
"We're optimistic that the deal will close in September," a Bcom3 spokesman said.
Full SEC review required
The acquisition was cleared in June by the European Commission and by Publicis shareholders, leaving only approval by U.S. regulators to complete the deal this summer.
The three-part deal -- also involving Japan's Dentsu -- was initially expected to close in June until the SEC sought a full review.