FCC Chairman Ajit Pai said he won't approve the Sinclair/Tribune acquisition as it's currently structured, saying Sinclair's plans for divested stations would violate the law.
Pai's decisions came after months of pressure from Democratic lawmakers, consumer advocacy groups, and industry lobby groups.
Pai has been repeatedly accused of making regulatory changes that benefit Sinclair; the FCC's inspector general in February agreed to investigate whether Pai has improperly coordinated with Sinclair on rule changes.
Pai's FCC previously rolled back broadcast TV station ownership limits, a move that at the time gave Sinclair a better chance of buying more stations.
When the FCC confronts disputed issues like these, the Communications Act does not allow it to approve a transaction.
"That's why analysts and investors rightly see today's news as potentially a fatal blow for this merger."