The Federal Communication Commission’s surprise move to block Sinclair Broadcast Group’s $6.6 billion acquisition of Tribune Media came after the head of a rival conservative news outlet discussed his opposition to the deal with President Trump, The Post has learned.

“I have discussed my opposition to the merger a few times with him,” Christopher Ruddy, founder and chief executive of Newsmax, told The Post on Wednesday, referring to his longtime friend, President Trump.

It is not known if Trump ever discussed the deal with FCC boss Ajit Pai — who on Monday said he has “serious concerns” about the merger and would move to block it.

Ruddy, who operates a right-leaning cable news network and website, has been a constant and outspoken critic of the Sinclair-Tribune deal.

Sinclair, with 191 broadcast stations in 89 markets, stands to pick up Tribune’s WGN, which some predict it will turn into a right-leaning national cable news network that could rival Newsmax.

Some M&A insiders claim Ruddy’s efforts were key to getting the FCC to block the deal.

On July 12, Newsmax’s lawyers at Boies Schiller Flexner filed papers with the FCC questioning Sinclair’s transparency — or lack thereof — in selling three key stations, including WGN, to less than an arm’s distance buyers, sources said.

Four days later, on July 16, the FCC moved to block the deal — citing some of the same transparency issues highlighted in the Boies letter.

“I think FCC Chair Ajit Pai’s decision is based on the rules and fair-mindedness,” Ruddy told The Post.

Still, the rivalry between Sinclair and Newsmax can’t be missed.

“They are in many ways going after the same audience,” said DC lobbyist David Goodfriend, who was working for several clients to stop the Sinclair merger.

Sinclair has been trying to recruit talent, including Bill O’Reilly, who appears weekly on Newsmax. The former Fox News Channel host was being wooed for a potential new cable news channel, a source close to the situation said.

“They could muscle me out” from getting on cable platforms, Ruddy told The Post, alluding to Sinclair having the bargaining power of owning local channels plus a national network when negotiating contracts.

Goodfriend said an encounter he had last fall spoke volumes about the growing rivalry between the two companies.

At an Oct. 12, 2017, conference former Trump White House official and Sinclair commentator Boris Ephsteyn approached Goodfriend and, knowing Newsmax was lobbying against the merger, asked him rhetorically if Newsmax didn’t already know “they are not going to stop this deal.”

Craig Aaron, from the left-leaning Free Press Action Fund, who is also opposed to the merger, said, “Newsmax was clearly influential.”

“Chris Ruddy is an influential guy that golfs with the president.”

Sinclair declined comment.