“The decision to muzzle a critic of this law is unacceptable while the U.S. opioid epidemic rages out of control,” Sen. Claire McCaskill (D-Mo.) wrote, referring to a law that curbed the Drug Enforcement Agency’s enforcement powers against the opioid industry. (Christopher Smith/for The Washington Post)

A high-ranking U.S. senator Thursday accused the Drug Enforcement Administration of silencing its chief administrative judge by barring him from publicly discussing a law that curbed the agency’s enforcement powers against the opioid industry.

U.S. Sen. Claire McCaskill (D-Mo.), the ranking Democrat on the Senate Homeland Security and Governmental Affairs Committee, told acting DEA administrator Robert W. Patterson that she was dismayed to learn that the judge would not be permitted to appear on Capitol Hill later this month.

“The decision to muzzle a critic of this law is unacceptable while the U.S. opioid epidemic rages out of control,” McCaskill wrote.

DEA spokeswoman Mary Brandenberger said, “We cannot speak to this.”

The Washington Post and “60 Minutes” revealed in a joint investigation last month that an early version of the legislation had been written by a drug industry lawyer. It was sponsored in the House by Rep. Tom Marino (R-Pa.). Sen. Orrin G. Hatch (R-Utah) negotiated the final version of the bill with the DEA. Two days after the media reports, Marino withdrew his nomination to be the nation’s next drug czar.

Both lawmakers have received substantial campaign contributions from political action committees representing the drug companies. Marino received nearly $100,000; Hatch $177,000, federal records show.

Following the passage of the bill last year, DEA Chief Administrative Law Judge John J. Mulrooney II wrote a law review article highly critical of the law. He said it makes it “all but logically impossible” for the agency to issue immediate suspension orders against drug companies in the most egregious cases because the standard of proof had been sharply increased. Those orders are dreaded by drug companies because they instantly shut down operations and all commerce in controlled substances.

“If it had been the intent of Congress to completely eliminate the DEA’s ability to ever impose an immediate suspension on distributors or manufacturers, it would be difficult to conceive of a more effective vehicle for achieving that goal,” Mulrooney wrote in his article, which is scheduled to be published this winter by the Marquette Law Review.

The judge also wrote that the law weakens another DEA enforcement tool known as orders to show cause. Those force companies accused of failing to report suspicious orders of narcotics to show why they should be allowed to continue to operate in the face of the alleged violations. Under the new law, those companies are allowed to submit corrective action plans before the DEA can sanction them.

Mulrooney likened that provision of the law to allowing bank robbers to “round up and return ink-stained money and agree not to rob any more banks.”

McCaskill is sponsoring legislation that calls for a repeal of the law and she has scheduled a roundtable discussion on Capitol Hill for Nov. 28. She has invited several former and current DEA officials, including Mulrooney. Because McCaskill is the ranking minority member on the Senate Homeland Security and Governmental Affairs Committee, she does not have the power to subpoena witnesses without approval from the Republican majority.

“Given these findings, and the unique expertise Judge Mulrooney has gained from years of adjudicating DEA administrative actions, I invited him to attend my forthcoming roundtable event,” McCaskill wrote in her letter to the DEA administrator. “Shockingly, however, DEA has declined to grant permission for Judge Mulrooney to attend.”

Sen. Charles E. Grassley (R-Iowa), the chairman of the Senate Judiciary Committee, has said he plans to hold a hearing into the law. Several Democratic senators have asked him to call the judge to testify before the panel.

“The committee is still working on the composition of the hearing, including panels and witnesses,” committee spokesman Taylor Foy said. “Chairman Grassley appreciates input from his colleagues, and will take it into consideration.”

On Tuesday, 44 state attorneys general called on Congress to repeal the law.

“The Ensuring Patient Access and Effective Drug Enforcement Act neither safeguards patient access to medication nor allows for effective drug enforcement efforts,” the bipartisan group of attorneys general wrote. “We urge you to repeal the act so that the public is protected and drug manufacturers and distributors may be held accountable for their actions.”

But efforts to repeal or rewrite the law have stalled on Capitol Hill because no key Republicans have signed on. Marino and Hatch, one of the most powerful members of the Senate, have fiercely defended the law, arguing that it ensures that patients gain access to the drugs they need while improving the DEA’s ability to do its job. They also note that the DEA approved the final language of the bill.

But senior DEA officials told The Post and “60 Minutes” last month that they fought the legislation for years, fearing it would undercut their enforcement efforts. They said they were forced to accept a bill they did not want or need.

“They would have passed this with us or without us,” said one senior DEA official, who spoke on the condition of anonymity for fear of antagonizing members of Congress who oversee the agency. “Our point was that this law was completely unnecessary.”