Merger talks between CBS and Viacom have hit a snag, sources tell CNBC.

CBS has not made a formal bid for Viacom after social issues raised a potential roadblock, the sources said. Specifically the two sides are trying to decide who the second in command will be at the combined company.

The battle is between Joe Ianniello, the chief operating officer of CBS, and Bob Bakish, the CEO of Viacom, the sources said.