President Donald Trump, a one-time football team owner, accelerated his criticism of the National Football League today by calling for a fan boycott, sparking strong objections from players and owners including a longtime friend and contributor.

Robert Kraft, chairman and chief executive officer of the NFL champion New England Patriots, said he was “deeply disappointed” by Trump’s comments Friday that “son of a bitch” players who refuse to stand during the national anthem to protest police brutality should be released by their teams.

Players locked arms, knelt or raised fists during today’s pregame renditions of the anthem, which were broadcast live at all games by the Fox and CBS networks. Jacksonville Jaguars owner Shahid Khan, who donated $1 million to Trump’s inaugural committee last year, locked arms with his players before his team’s game against the Baltimore Ravens in London. Several other owners joined their players on the field while most of the Pittsburgh Steelers stayed in their locker room during the anthem.

The criticisms, directed primarily at black athletes, came after Trump repeatedly equated the actions of both sides after the death of a woman who was protesting against a demonstration by neo-Nazis, white supremacists and Confederate heritage groups in Charlottesville, Virginia.

Critical Week

They also come at the start of a critical week for some of Trump’s key legislative priorities, with Republicans’ latest and possibly last attempt to repeal and replace the Obamacare health care law on the brink of defeat and negotiations beginning in earnest on a tax package.

Treasury Secretary Steven Mnuchin defended Trump’s comments and called on the NFL owners to enact a rule requiring players to stand during the national anthem.

“This is about respect for the military and the first responders and the country,” Mnuchin said on ABC’s “This Week” program. “They have the right to have their First Amendment off the field. This is a job and the employers have the right, when the players are working, to have rules.”

Owners’ Support

Trump’s new campaign also may jeopardize the support he has enjoyed since the early days of his campaign from a number of CEOs and NFL owners — one of whom, Woody Johnson of the New York Jets, was named Trump’s ambassador to the U.K.

“There is no greater unifier in this country than sports, and unfortunately, nothing more divisive than politics,” said Kraft, who also donated $1 million to Trump’s inaugural and sat with the president at dinner when he hosted Japanese Prime Minister Shinzo Abe at his Mar-a-Lago resort in February. “I think our political leaders could learn a lot from the lessons of teamwork and the importance of working together toward a common goal.”

The president doubled down on his comments on Twitter even after being rebuked by NFL Commissioner Roger Goodell and DeMaurice Smith, head of the NFL Players Association. “If NFL fans refuse to go to games until players stop disrespecting our Flag & Country, you will see change take place fast,” Trump said on Twitter Sunday morning. “Fire or suspend!”

In a second tweet he added, “NFL attendance and ratings are WAY DOWN. Boring games yes, but many stay away because they love our country. League should back U.S.”

The national anthem protests began in August 2016, when former San Francisco 49ers quarterback Colin Kaepernick kneeled before a pre-season game. Kaepernick was joined in his protest by some teammates and players on other teams as the season progressed.

Kaepernick opted out of his contract with the 49ers in March and hasn’t been signed by another team, although the protests have continued this season.

‘Lack of Respect’

NFL Commissioner Goodell, without mentioning Trump, said Saturday that “divisive comments” weren’t helpful.

“The NFL and our players are at our best when we help create a sense of unity in our country and our culture,” Goodell said in a statement. “Divisive comments like these demonstrate an unfortunate lack of respect for the NFL, our great game, and all of our players.”

Trump himself was once owner of the New Jersey Generals of the long-defunct United States Football League, which fought a losing battle against the NFL.

‘Little Ding’

The president also raised eyebrows Friday by saying that penalties for hard hits in the NFL are “ruining the game,” as the league attempts to respond to evidence of long-term brain injury causing premature deaths and disability to some of its players.

Trump’s comment came a day after news that Aaron Hernandez, the former New England Patriots player convicted of murder who hanged himself in a Massachusetts jail in April at age 27, had been found to suffer from a severe case of the degenerative brain disease chronic traumatic encephalopathy (CTE) associated with repeated concussions.

Trump made similar comments about the NFL at least twice in 2016, deriding concussions as “a little ding on the head” and lamenting the demise of “violent, head-on” tackles.

A recent study published in the New England Journal of Medicine found that all but one of 111 former NFL players whose brains had been inspected had evidence of CTE, which can only be diagnosed post-mortem.