President Trump on Thursday accused The Boston Globe of “COLLUSION” with other newspapers, as hundreds of outlets launched coordinated editorials hitting back at his attacks on members of the press.

“The Boston Globe, which was sold to the the Failing New York Times for 1.3 BILLION DOLLARS (plus 800 million dollars in losses & investment), or 2.1 BILLION DOLLARS, was then sold by the Times for 1 DOLLAR. Now the Globe is in COLLUSION with other papers on free press. PROVE IT!” Trump tweeted.

Minutes later, Trump seemed to soften his tone, but maintained his accusations that the press pushes a “political agenda.”

“There is nothing that I would want more for our Country than true FREEDOM OF THE PRESS. The fact is that the Press is FREE to write and say anything it wants, but much of what it says is FAKE NEWS, pushing a political agenda or just plain trying to hurt people. HONESTY WINS!”

The president’s tweets came as more than 300 publications across the country -- most of which supported Hillary Clinton in 2016 -- participated in the effort, initially organized by The Boston Globe. The Globe urged editorial boards of major and local newspapers to publish columns promoting freedom of the press.

“THE FAKE NEWS MEDIA IS THE OPPOSITION PARTY. It is very bad for our Great Country….BUT WE ARE WINNING!” Trump tweeted earlier Thursday morning.

The Globe’s piece, published Thursday, titled “JOURNALISTS ARE NOT THE ENEMY,” said replacing “a free media with a state-run media” is the “first order of business for any corrupt regime taking over a country.”

“Today in the United States we have a president who has created a mantra that members of the media who do not blatantly support the policies of the current U.S. administration are the ‘enemy of the people,’” the editorial board wrote. “This is one of the many lies that have been thrown out by this president much like an old-time charlatan threw out ‘magic’ dust or water on a hopeful crowd.”

The Globe’s editorial board wrote that press freedom is “under serious threat. And it sends an alarming signal to despots from Ankara to Moscow, Beijing to Baghdad, that journalists can be treated as a domestic enemy.”

The Globe, on Thursday, also changed its Twitter avatar to an image of a hashtag in red, all-capital letters: #FREEPRESS.

The Globe’s column was one of hundreds circulating throughout the U.S. on Thursday.

The president has routinely mocked and attacked media outlets—like CNN, NBC, The New York Times, and The Washington Post—over critical stories that he often disputes.

The tensions between Trump and the media, though, have been flaring ever since the campaign. By one count, of the 100 biggest newspapers in the U.S., 57 endorsed Clinton for president, four endorsed Libertarian Party candidate Gary Johnson, and only two endorsed Trump.

Politico’s senior media writer Jack Shafer wrote in his own op-ed that the coordinated editorial attack Thursday is “sure to backfire,” and likely will provide extra ammunition for Trump.

“It will provide Trump with the circumstantial evidence of the existence of a national press cabal that has been convened solely [to] oppose him,” Shafer wrote. “Trump will reap enough fresh material to wale on the media for at least a month.”

Shafer pointed out that most editorial boards didn’t support Trump in the first place.

“Editorial-page sentiment against Trump remains largely unchanged since the election, making the call for a collective reprimand all the more pointless,” he wrote.

Fox News' Brian Flood contributed to this report.