Dozens of Democratic and Republican lawmakers are calling on the White House to thwart the Drug Enforcement Administration’s moves to ban kratom, claiming the herbal opioid substitute was rescheduled in violation of procedural law.

The lawmakers, organized by Reps. Mark Pocan (D-Wis.) and Matt Salmon (R-Ariz.), asked Office of Management and Budget Director Shaun Donovan on Monday to “use your statutory authority” to the delay implementation of the rule change.

Fifty-one US Representatives, including 22 Republicans, signed the letter, according to The Huffington Post.

Under the edict issued late last month by the DEA, kratom is set to be considered a Schedule I controlled substance on Friday—on par with heroin, cocaine, and, controversially, cannabis.

“The Agency did not provide any public comment process for this significant regulatory decision, which will restrict consumer choice and access to internationally recognized herbal product,” Monday’s letter stated.

“We believe the Office of Information and Regulatory Affairs (OIRA), under you jurisdiction, must utilize its statutory authority to manage and oversee this specific regulatory action to ensure the DEA is not violating federal law,” the request added.

As the lawmakers noted, research has shown that kratom has promise as a proven safe treatment for opioid withdrawal.

They also said that federally-funded researchers have applied to patent a kratom extract, mitragynine, “as a useful treatment for other addictive drugs besides opiate derivates.”

“The DEA’s decision to place kratom as a Schedule I substance will put a halt on federally funded research and innovation surrounding the treatment of individuals suffering from opioid and other addictions—a significant public health threat,” they told Donovan.

The letter was sent by the lawmakers alongside a request to DEA Acting Administrator Chuck Rosenberg, calling on the agency to reverse its decision.

When the DEA issued its announcement about kratom rescheduling, it said there were fifteen “kratom related deaths between 2014 and 2016”–claims that have been challenged, upon scrutiny. Most prescription opiods are considered Schedule II, by the DEA, despite killing tens of thousands of people in the US annually.