Sen. Thom Tillis, R-N.C., told NBC News’ “Meet the Press” on Sunday that President Donald Trump’s decision to ease sanctions on Russia to allow it to release diesel fuel to the global market may be breaking the law.

“I do believe there’s a legitimate case for saying the president’s not following the law,” Tillis said.

Trump announced in a Friday post on Truth Social that Russia would “immediately supply” hundreds of thousands of tons of diesel fuel to the global marketplace, with more than 1 million additional tons soon on the way. The move drew sharp condemnation from Ukraine and critics of the Trump administration.

Following Russia’s invasion of Ukraine, lawmakers took a series of steps to try to financially punish the Kremlin. In 2022, the Senate unanimously passed a bill to ban Russian oil imports, and Congress has not made changes to the law to reflect the president’s announcement.

Asked by moderator Kristen Welker whether he believes the president is breaking the law with his Russia deal, Tillis said, “I believe that he may be.”

“We were very clear that Russia is the aggressor,” he added. “Russia is the one who can end this war by backing out of territory that they occupied.”

The White House didn’t immediately respond to a request for comment on the senator’s remarks.

Tillis referenced year-end congressional funding negotiations when asked what the Senate could do if Tillis believes Trump is breaking the law.

“If the president wants my support, which I believe he should get for funding military operations and year-end funding beyond baseline funding, I think the president needs to understand this is a problem, and I’m not the only Republican concerned with this,” he said.

Asked whether Trump’s deal with Russian President Vladimir Putin was putting American lives at risk, Tillis said, “It absolutely will,” pointing to Russian funding of mercenaries and the Kremlin’s relationship with Iran.

Tillis has just months remaining before his term expires. His retirement from the Senate created a high-profile battleground opening. Democrats are eyeing his seat as a prime target to flip as they seek control of the chamber.

Tillis has been highly critical of aspects of the Trump administration, including the performance of Defense Secretary Pete Hegseth. Tillis, who voted for Hegseth’s confirmation, now says he regrets his vote.

Tillis on Sunday condemned the Pentagon’s plan to livestream the execution by firing squad of Nidal Hasan, who was convicted in the 2009 mass shooting in Fort Hood, Texas.

Tillis said that the livestream plans would radicalize people and be used by terrorist groups as a recruiting tool.

“The Fort Hood shooter should be put to death, but there’s a way to deal with this that’s proper, and there’s a way to deal with this that’s more improper than I have ever observed in my life,” he said.

“This is not who we are, and it’s another example of why Pete Hegseth, in all of his bravado, needs to get the hell out of the Department of Defense, because he is a failed leader, and we need strong leadership supporting President Trump right now,” he added.