Tribune Media and Sinclair Broadcast Group both slumped after the head of the Federal Communications Commission said he has “serious concerns”  about Sinclair’s plan to buy Tribune.

Right-leaning TV station operator Sinclair has proposed selling some of its own TV stations as part of the $3.9 billion deal, but FCC Chairman Ajit Pai said Sinclair would continue to control them in practice, which would violate the law.

Tribune Media plunged 15 percent to $32.80 and Sinclair sank 5.2 percent to $31.23.

Sinclair is already the largest operator of local TV stations in the U.S.

Both companies operate stations in North Carolina.

“Based on a thorough review of the record, I have serious concerns about the Sinclair/Tribune transaction,” Pai said in a statement. “The evidence we’ve received suggests that certain station divestitures that have been proposed to the FCC would allow Sinclair to control those stations in practice, even if not in name, in violation of the law.

“When the FCC confronts disputed issues like these, the Communications Act does not allow it to approve a transaction. Instead, the law requires the FCC to designate the transaction for a hearing in order to get to the bottom of those disputed issues. For these reasons, I have shared with my colleagues a draft order that would designate issues involving certain proposed divestitures for a hearing in front of an administrative law judge.”