Elizabeth Warren and Bernie Sanders are among a group of five senators who slammed Novartis' AveXis for submitting manipulated data to the FDA ahead of the approval of its gene-therapy drug.

The FDA revealed the data-manipulation issue earlier this week, saying that it affected only a small portion of product-testing data and that the regulator was confident the drug, Zolgensma, should keep being sold.

"This scandal smacks of the pharmaceutical industry's privilege and greed, and Americans are sick of it," the senators wrote in a letter to Ned Sharpless, the acting head of the FDA.

Novartis said it first learned about the data problem in March. But the Swiss drug giant informed the FDA months later, after the gene therapy was approved, the FDA said.

The five senators encouraged the FDA to "use your full authorities to hold AveXis accountable for its malfeasance," adding that "anything short of a forceful response would signal a green light to future pharmaceutical misbehavior."

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Five senators, including Elizabeth Warren and Bernie Sanders, are slamming the Swiss drug giant Novartis for submitting manipulated data to the US Food and Drug Administration — which was part of a package that led to its $2.1 million drug getting approved.

The FDA made the data problem public earlier this week. It appears to affect only a small amount of data, and the FDA said it "remains confident" the drug, Zolgensma, should still be sold.

In the pharmaceutical industry, where data is the basis for approval of life-or-death drugs, data manipulation is serious business. The controversy has bubbled up this week, magnified by the visibility of Zolgensma, which at $2.1 million is the most expensive drug in the world, as well as the high profile of Novartis, whose new, young, and charismatic CEO has sought to transform the company.

"This scandal smacks of the pharmaceutical industry's privilege and greed, and Americans are sick of it," the senators wrote in the letter, which was addressed to Ned Sharpless, the FDA's acting head. In addition to Warren and Sanders, both 2020 presidential hopefuls, the letter was also signed by Sens. Richard Durbin, Tammy Baldwin and Richard Blumenthal, who are all Democrats.

Novartis declined to comment on the letter from the senators.

Data-manipulation timeline provokes outrage from senators

The timeline of Novartis' disclosure to the FDA also inspired ire from the senators. Novartis heard allegations of data manipulation in March, before Zolgensma was approved in May. But the drugmaker disclosed it to the FDA a month after the approval, on June 28, the FDA said.

Read more: A top executive at Swiss drug giant Novartis told us the inside story of the $2.1 million price tag for the most expensive drug in the world

In a conference call with investors this week, Novartis CEO Vas Narasimhan said the company had been investigating the allegations itself and denied that it had been influenced by the timing of Zolgensma's approval. The data manipulation was carried out by only a few people, and Novartis would "exit" them, he said.

The drugmaker "tried to do all of the right things," Narasimhan said. "There will be bumps on the road, we'll never be perfect, but we will be relentless in trying to keep improving and being the most highly respected company in our industry."

But the senators disagreed, calling Novartis's actions "unconscionable" and urging the FDA to take action. The regulator has previously said it could impose either civil or criminal penalties.

"We urge you to use your full authorities to hold AveXis accountable for its malfeasance," they said. "Anything short of a forceful response would signal a green light to future pharmaceutical misbehavior."

The senators also asked the FDA why it had scrapped a regulation proposed last fall, which would have required healthcare companies to quickly report falsified data, and whether that regulation would be reissued because of the AveXis news.