New Delhi, July 15 -- LOS ANGELES - A day after twelve state attorneys general moved to block it and days after the Justice Department waved it through without conditions, the $111 billion merger between Paramount Skydance and Warner Bros. Discovery faces its sharpest legal challenge yet. The Writers Guild of America filed a federal antitrust complaint Tuesday in San Francisco, arguing that combining two of Hollywood's largest studios would give a single buyer unprecedented control over the careers and paychecks of the writers who build the industry's programming slate.

The WGA's case rests on four years of its own employment data. According to figures the union compiled and filed with the Northern District of California, Paramount and W...