The Federal Communications Commission (FCC) on Wednesday voted unanimously to send the merger between Sinclair Broadcast Group and Tribune Media before an administrative law judge, a process that could doom the $3.9 billion deal.

FCC Chairman Ajit Pai had proposed the move earlier this week, saying he had “serious concerns” about whether the merger is legal.

The agency said in an announcement Wednesday night that the full text of the order that was voted upon would likely be released Thursday.

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Pai’s decision shocked many observers. Since he became chairman in January 2017, he has pushed a deregulatory agenda that’s included scrapping media ownership rules that would have gotten in the way of the Sinclair-Tribune deal.

Sinclair responded to his proposal on Wednesday with a revised plan to sell off certain stations from the combined company in order to get it under a congressionally-mandated ownership limit.

The 4-0 vote Wednesday evening appears to be a rejection of those concessions.