The chief executive of Valeant Pharmaceuticals has been ordered to give evidence about rising drug prices to a Senate committee.
Michael Pearson was ordered to appear on 27 April to testify about the practice of buying the rights to old medicines and raising prices.
Valeant is facing three separate federal investigations into its business practices.
Shares fell more than 7% on Monday in New York following the announcement.
The Senate Aging Committee sent letters to the heads of several other drug makers asking them to testify as well.
In November, Senator Claire McCaskill, who is leading the investigation, said she was concerned that the practice was "price-gouging".
"Some of the recent actions we've seen in the pharmaceutical industry - with corporate acquisitions followed by dramatic increases in the prices of preexisting drugs - have looked like little more than price gouging," she said.
Valeant is not alone in the practice of buying existing drugs and raising the prices. Its focus on acquisitions rather than development of new drugs, however, has raised questions about the Canadian company's long-term viability.
John Hempton of Bronte Capital, who is betting against the stock, told the BBC: "Saying Valeant's problems are from its business model is against the point because other pharma companies are still working on that model. But raising prices so fast was never going to be acceptable in the long run."
The company's New York-listed shares have plunged more than 70% this year.
Last week, Valeant announced that Mr Pearson would step down as chief executive as soon as a replacement could be found.
Activist investor Bill Ackman, one of Valeant's largest shareholders and most outspoken supporters, has joined the company's board.