President Donald Trump is facing growing backlash over his plan to import diesel from Russia, with some Republican and Democratic lawmakers insisting that the controversial deal “violates” the law.

Congress four years ago passed the Ending Importation of Russian Oil Act, which prohibits U.S. imports of Russian-origin energy products covered by Chapter 27 of the Harmonized Tariff Schedule, including diesel. Democratic Rep. Lloyd Doggett of Texas, the bill's chief sponsor, argued Monday that Trump is “directly violating that law” by “lifting sanctions to permit the first Russian diesel imports into the United States since the law took effect, without satisfying the specific legal conditions it requires.”

He suggested the lack of congressional oversight on Trump’s deal with Putin renders it unlawful, and noted how the plan showcases a sharp turn from Washington, as it comes just weeks after Trump signed a sweeping Russia sanctions bill intended to target the country's financial institutions and the energy industry, which has largely financed the assault on Ukraine. The sanctions bill was named after Lindsey Graham, the late Republican Senator who spent the final year of his life building support for the measure.

“Russia can [now] export fossil fuel to the U.S. after Trump violated the specific provisions of a federal statute,” Doggett said on Tuesday in a statement to TIME. “While offering little benefit for Americans, this unlawful action will provide substantial new funding for Putin‘s war machine to continue murdering Ukrainian civilians.”

Doggett’s concerns match those of Republican Sen. Thom Tillis of North Carolina, who told NBC’s Meet the Press over the weekend that he believes “there’s a legitimate case for saying the President’s not following the law.”

Tillis was one of seven Senators who publicly urged the Administration on Sunday to “immediately reverse course” on the agreement announced Friday, arguing that it goes against the 2022 law.

“Congress explicitly banned Russian energy imports in 2022 to prevent American dollars from financing Putin’s brutal war against Ukraine,” read the statement co-signed by Republican Senators Lisa Murkowski of Alaska, Susan Collins of Maine, Thom Tillis of North Carolina, and John Curtis of Utah, alongside Democratic Senators Jeanne Shaheen of New Hampshire, Ron Wyden of Oregon, and Richard Blumenthal of Connecticut.

“President Trump’s decision to allow Russian diesel imports to the U.S. runs directly counter to that law. The Administration has also failed to consult with Congress or submit any explanation to justify its decision as required by statute,” they said.

In a letter sent to Trump on Tuesday, Tillis, Collins, and Murkowski, were joined by fellow Republican Senators Mitch McConnell of Kentucky, John Cornyn of Texas, and Alan Armstrong of Oklahoma alongside six Democratic Senators as they told the President the deal “is a gift to our adversary and a betrayal of our Allies [and] should be rescinded.” The letter came a day after Trump publicly dismissed the criticism stemming from within his own party.

"Well, I think these are Republicans that can't really be serious," he told reporters at the White House. “Anything that could help our farmers, our ranchers, I like.”

Trump’s deal to "immediately" supply 300,000 tons of diesel to American and global markets comes as he faces growing political pressure ahead of the November midterms. Spiraling energy costs have become a key concern for voters, threatening to undermine Republican efforts to maintain their majorities in Congress. The financial upheaval has meant that Trump risks losing his hold on farm country. However, experts are skeptical that an influx of Russian fuel will bring relief to struggling Americans, given how short the supply is due to the disruption in the Strait of Hormuz.

While some lawmakers also predict the impact on American consumers will be slight, the key sticking point for many centers on whether Trump’s diesel deal with Putin violates the 2022 law, with some Republicans and Democrats insisting that Trump is pushing the limits of presidential authority. Here’s what to know about the debate—and where legal experts stand on the matter.

According to the 2022 law, what must happen for the import ban on Russian diesel to be lifted?

While Presidents typically have broad authority to waive sanctions, Congress placed specific limits on that power in the April 2022 legislation, says Kristen Eichensehr, a professor of law at Harvard Law School.

“In many sanctions authorities, the President has broad authority to waive imposition of the sanctions or to issue licenses that basically provide an exception to the sanctions,” she tells TIME. “The [2022 act] is an unusual law, given how careful and specific Congress was in providing that the President lacks that flexibility.”

Under Section 3 of the legislation, the President must first consult with the House Ways and Means and Foreign Affairs Committees, along with the Senate Finance and Foreign Relations Committees, and submit a report at least 45 days before providing the required certification.

Lawmakers have argued that the Administration has failed to follow this process.

“The President has to provide a certification to Congress in advance before lifting the prohibition,” says Eichensehr, pointing to the specific criteria set out in the wording of the law.

The law requires a determination by the President to Congress that the Russian Federation has withdrawn and ceased hostilities accepted by Ukraine; poses no immediate threat to any NATO member; and recognizes the right of the Ukrainian people to freely and independently choose their own government.

But Eichensehr insists that these are “not certifications that the President could make at the current moment” because “none of those things have happened, and that's the main restriction in the law.”

Even if all these conditions were met, the legislation would still require the President to wait an additional 90 days before the termination of the import ban could take effect, during which, Congress could enact a joint resolution of disapproval.

“On the substance, the President cannot, as a factual matter, make the certifications because Russia is still attacking Ukraine,” says Eichensehr. “As a procedural matter, [because he reportedly has not consulted Congress], he hasn't followed the process that the law sets out.”

Edward Swaine, a research professor at George Washington University Law School, suggests these restrictions were put in place to ensure that “when the President and the Treasury Secretary decide that circumstances have changed, they go back and explain this to Congress, and give it notice so that it can disagree.”

“The President is supposed to make this determination that Russia has withdrawn its forces and doesn't pose any further threat of aggression. These are fairly high standards,” he tells TIME, noting that the statue provides “Congress with adequate notice to allow it to generate a joint resolution of disapproval.”

“They don't want the President to be able to change this regime on a whim, and so I imagine Congress looking at this action and justifiably thinking that this is inconsistent,” he adds.

Treasury says the diesel deal is being carried out within the legal authorities

Treasury Secretary Scott Bessent has defended the legality of the agreement, insisting that the Trump Administration is acting within its existing legal authority to help bring energy prices down.

“We’re doing it with all the legal authorities we have, so anyone in Congress who says that—whether it’s an old bill or the current Lindsey Graham bill—prohibits us from doing it, is wrong,” he told Fox News on Sunday, without elaborating on which legal authorities he was referring to.

On Friday, the Treasury Department’s Office of Foreign Assets Control (OFAC) issued a temporary general license authorizing transactions involving Russian diesel fuel, including its importation, until April 7, 2027.

Swaine says that the Administration could argue that “the general license isn't [a] termination of the statutory prohibition; it's a suspension.”

“The [Treasury] Secretary could say this isn't the same thing as ending the prohibition on imports, it's just suspending it until April,” says Swaine. “The second thing [the Administration] could say is that it doesn't apply to all affected products, just a subcategory concerning diesel fuel, so there's [potentially] a difference between the actions that are required for the President to terminate the entire program and the actions that the Secretary is taking here.”

Responding to claims on social media that Bessent and the White House had broken the law, the Office of the Under Secretary for Terrorism and Financial Intelligence, part of the Treasury, insisted that the Administration had followed established procedures.

“The granting of this general license is consistent with similar actions previously taken by OFAC and is in compliance with all applicable laws,” the office said over the weekend.

The OFAC permitted transactions involving Russian oil and petroleum products already loaded on vessels, including from vessels previously under U.S. sanctions, to Indian ports in March; the office had also allowed the entry of specified diamonds in August that had been outside Russia before set cutoff dates under a previous Executive Order.  

TIME has reached out to the White House and Treasury Department for comment.

How Congress could challenge Trump's diesel deal

Lawmakers could pursue congressional oversight and other political measures to challenge the Administration’s decision.

Republican Rep. Brian Fitzpatrick of Pennsylvania has already announced plans to introduce “bipartisan legislation to block any and all purchases of Russian oil” under the proposed “Ronald Reagan Peace Through Strength Act.” Rep. Don Bacon of Nebraska, a Republican who has clashed with Trump on other high-profile issues, said he has agreed to co-sponsor the bill, because “Congress must make a stand.”

However, experts tell TIME what Congress is able to do may be limited to more of a symbolic display rather than anything that can move the needle.

“There's limited ability of Congress to do much besides pass legislation and politically enforce that,” says Swaine, suggesting that methods such as “withholding money, appropriations, and hearings” could be used if the situation escalated to that point.