merger of equals.
"There are mechanisms in place in the first few years to protect the parity of management so it should be fine in the transition period. But in these kinds of mergers, there are always tensions. Usually one side or the other eventually imposes its way of doing things on the other."
The new group will also have to get antitrust clearance from authorities in around 45 countries. "We've looked at the antitrust issues very carefully and are not expecting anything that would prevent us from going forward," said Wren.
Morningstar analyst Corty said it was unlikely the two companies would have progressed to this stage if they had doubts about getting approval.
Others were less optimistic. Bert Foer, head of American Antitrust Institute, predicted that clients of the two advertising giants would object to the deal and that media companies that depend on advertising to survive would complain to antitrust authorities. Asked about regulatory approval, he said: "I don't think they should get it."
The main competition issue will be in media buying, where advertising agencies purchase TV or print ads on behalf of customers. Pivotal Research analyst Brian Wieser estimates that Publicis Omnicom will account for almost 20 percent of global media spending and closer to 40 percent in the United States.
To face such concerns, the groups might have to sell small brands in some countries, said a person close to the talks.
It is unlikely France will derail the deal despite the fact that a national champion is tying the knot with an American rival. Levy said the government had already expressed support for the merger.