U.S. Sens. Bernie Sanders and Elizabeth Warren have been harsh critics of the pharmaceutical industry in general. Now they've joined hands with three other senators to go after one pharma company in particular.

In a letter to the FDA, five Democrats, led by Sen. Richard Durbin of Illinois, blasted Novartis and its AveXis unit for submitting—and failing to quickly disclose—manipulated data that helped its $2.1 million spinal muscular atrophy gene therapy Zolgensma win an FDA approval.

They're not just looking for a public scolding. They're calling on the FDA to throw the book at the Swiss drugmaker and the gene therapy unit it bought last year. And their criticism could well lead the FDA to revive a data-disclosure rule it nixed in October.

"We urge you to use your full authorities to hold AveXis accountable for its malfeasance, including through all appropriate criminal, civil, and regulatory actions against the company," the senators wrote in a letter (PDF) addressed to FDA’s acting commissioner, Ned Sharpless. "Anything short of a forceful response would signal a green light to future pharmaceutical misbehavior."

The FDA last week revealed that Novartis had used falsified animal testing data in its Zolgensma drug application package. While the senators criticized the submission itself as "unconscionable," they also took issue with Novartis’ disclosure timeline.

By Novartis’ account, it became aware of the data problem in March and confirmed the allegation internally in early May, ahead of Zolgensma’s approval on May 24. But the company didn’t inform the FDA until June 28, after it completed an internal investigation.

Meanwhile, the five senators are also calling on Sharpless to explain why the FDA decided in October 2018 to withdraw a regulation that would have required drugmakers to promptly report suspected falsified data, and whether the FDA plans to reinstate it in the wake of the AveXis case.

In a conference call with investors, Novartis CEO Vas Narasimhan denied the delay had anything to do with the timing of the FDA review. After confirming the allegations from an internal whistleblower in May, the company had also gone on to find out more details before handing the FDA the "technical assessment," he said.

Novartis "tried to do all of the right things," Narasimhan said. However, the senators characterized the drugmaker’s lag in communication as "knowingly misleading the FDA in a rush to make a profit."

The bad data were so far only linked to mouse assays used only for initial product testing, not for commercial product release, Novartis has said.

The FDA agreed with Novartis that Zolgensma should stay on the market given the evidence around the drugs’ effectiveness and safety profile in human clinical trials. However, the agency has also said it takes "the integrity of the product testing data […] very seriously." As such, the FDA said it’s considering possible civil or criminal penalties against Novartis.

Sanders and Warren are both outspoken critics of the drug industry. In December, Warren and Rep. Jan Schakowsky introduced bills that aim to lower drug prices by asking the federal government to manufacture generic drugs. That proposal came shortly after Sanders introduced his own Prescription Drug Price Relief Act that would tie U.S. drug prices to those from other developed countries.

Warren recently went after former FDA commissioner Scott Gottlieb’s transition to Pfizer’s board, saying the move "smacks of corruption." And Sanders just paired with Rep. Elijah Cummings in asking the Department of Justice to prioritize a generic drug price-fixing investigation.

Novartis itself has been embroiled in several reputational crises lately, including bribery and doctor kickback allegations in several countries, including the U.S. Not to mention the payment to President Donald Trump’s former personal lawyer Michael Cohen, which hit headlines even outside of the life sciences world.

Since Narasimhan took over the CEO job, he has made rebuilding trust with society a top priority at Novartis. "It’s a long, long road and sometimes it’s bumpy," he acknowledged during the Zolgensma call.