President Trump stepped up his Twitter criticism of the NFL on Monday morning, while praising NASCAR and its fans for not “disrespecting our Country” -- as the president's feud with the sports world took yet another turn.

Unlike many NFL players who locked arms, kneeled or even stayed in their locker rooms during the national anthem, NASCAR drivers did not protest "The Star-Spangled Banner" during their Cup Series race in New Hampshire this weekend.

“So proud of NASCAR and its supporters and fans. They won’t put up with disrespecting our Country or our Flag –they said it loud and clear!” Trump tweeted Monday morning.

Richard Petty, a former NASCAR driver and now team owner, told the Associated Press on Sunday that he wouldn’t accept any protest from his drivers.

“Anybody that won’t stand up for the anthem ought to be out of the country,” Petty said. “Period.”

Another owner, Richard Childress, said that his team members should “respect the country we live in.”

A NASCAR team executive said that the league currently has “no policy” on the issue of protesting the National Anthem, as it had never come up for them in the past.

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Trump contrasted that response Monday with the widespread protests in the NFL, which took off after the president seemed to take a shot during a political speech last week at Colin Kaepernick's anthem-kneeling.

“Many people booed the players who kneeled yesterday (which was a small percentage of total). These are fans who demand respect for our Flag!” Trump tweeted Monday.

More than 100 NFL players from teams across the country kneeled or locked arms after Trump slammed such protesters, calling for their suspension or firing should they show disrespect for the flag.

“If NFL fans refuse to go to games until players stop disrespecting our Flag & Country, you will see change take place fast,” Trump tweeted Sunday morning ahead of the games. “Fire or suspend!”

The feud began on Friday during the president’s rally in Alabama, when he first called for players to be fired if they disrespected the flag.

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“Wouldn’t you love to see one of these NFL owners, when somebody disrespects our flag, to say ‘get that son of a b –off the field right now? Out! He’s fired! He’s fired!” Trump said to the crowd Friday evening, drawing criticism from NFL Commissioner Roger Goodell.

“Divisive comments like these demonstrate an unfortunate lack of respect for the NFL, our great game and all of our players, and a failure to understand the overwhelming force for good our clubs and players represent in our community,” Goodell said.

The controversy over standing for the national anthem began during last season, when former San Francisco 49ers quarterback Kaepernick refused to stand during "The Star-Spangled Banner" to protest police brutality against the African-American community. Kaepernick is currently a free agent and has yet to be drafted to a team.

“The issue of kneeling has nothing to do with race. It is about respect for our Country, Flag and national anthem. NFL must respect this!” Trump tweeted Monday morning, but moments later, pivoted to important agenda items for his administration.

“The White House never looked more beautiful than it did returning last night,” Trump said. “Important meetings taking place today. Big tax cuts & reform.”

The Trump administration hopes to notch legislative victories in the coming days -- with a controversial ObamaCare overhaul possibly coming to the Senate floor this week, and tax reform on the horizon.

The president's NASCAR praise, however, could be short-lived. Dale Earnhardt Jr. tweeted Monday: "All Americans R granted rights 2 peaceful protests ... Those who make peaceful revolution impossible will make violent revolution inevitable-JFK."

Fox News' Katherine Lam contributed to this report.