France’s Publicis and U.S.-based Omnicom (OMC) agreed to terminate their $35 billion merger, citing “difficulties” in completing the transaction on time.  

The deal, announced in July as a strategic move that would improve both of their positions in the digital advertising arena, would have created the world’s largest advertising agency.

In a joint statement, Publicis CEO Maurice Lévy and Omnicom chief John Wren said the remaining challenges and slow pace of progress created a “level of uncertainty detrimental to the interests of both groups and their employees, clients and shareholders.”  

The parties have released each other for all obligations and neither will be responsible for termination fees. They will go back to operating as rivals.

In an interview with Reuters, Wren said the deal collapsed over disagreements over the structure of the merger. Omnicom wanted their people to fill all the top spots, including CEO, CFO and general counsel, and Wren said he thought that request “went too far.”

“I was not ready to cede on this point,” Wren told Reuters.

Shares of Omnicom fell 1.8% to $66.20 in pre-market trade. They are down about 6% over the last six months.  

Follow Jennifer Booton on Twitter at @Jbooton