Regulators accused Sinclair Broadcast Group Inc. of misleading them as it sought approval to buy Tribune Media Co. — and sent their companies' proposed $3.9 billion merger to the uncertain future of a hearing.

The U.S. Federal Communications Commission asked whether Sinclair was in fact the hidden buyer in a proposal to sell Chicago's WGN-TV to an automobile executive with no prior broadcast experience. The agency also questioned ties between the Maryland-based broadcaster and a buyer proposed for stations in Dallas and Houston.

The planned station sales were set at what appeared to be below-market prices, and Sinclair was poised to remain in control of the properties despite the transactions, the FCC said. Sinclair had proposed divestitures to avoid exceeding ownership limits after buying Tribune's 42 television stations.