France's two biggest private broadcasters are closing ranks to fend off the meteoric rise of U.S. streaming platforms, hoping the desire for a national champion that can take on global video-on-demand giants will trump domestic antitrust concerns.

Announcing their merger on Monday, TF1 and M6 stressed their move was a response to the accelerating challenges from global platforms, saying the deal was critical to ensure the long-term independence of French content creation.

A combined TF1 and M6 would, however, hold sway over three-quarters of France's TV advertising market, a threshold likely to trigger alarm bells at the country's antitrust authority.

The antitrust challenge facing the French broadcasters could be a test case for potential alliances elsewhere in Europe, such as Germany where Bertelsmann (BTGGg.F) has called for the creation of national champions to challenge streaming rivals.