President Trump said Tuesday it was “disgraceful" that federal regulators have blocked Sinclair Broadcast Group Inc.’s $3.9 billion acquisition of Tribune Media Co. , taking sides against the Federal Communications Commission in the politically charged deal.

“So sad and unfair that the FCC wouldn’t approve the Sinclair Broadcast merger with Tribune,” tweeted Mr. Trump. He said the acquisition would have created a “much needed conservative voice by and for the people.”

Mr. Trump also referenced the 2011 merger of Comcast Corp. and NBC Universal, which the FCC allowed to go through. NBC is one of the networks Mr. Trump regularly criticizes.

Mr. Trump tweeted: “Liberal Fake News NBC and Comcast gets approved, much bigger, but not Sinclair. Disgraceful!”

The FCC didn’t immediately respond to a request for comment.