A U.S. congressional committee has demanded that former drug executive Martin Shkreli appear at a hearing on drug prices to testify about his former company's decision to raise the price of a lifesaving medicine by more than 5,000 percent, congressional aides said on Wednesday.

Shkreli, who is separately facing federal criminal charges that he defrauded investors, has been served with a subpoena to appear on Jan. 26 before the U.S. House of Representatives' Committee on Oversight and Government Reform, the aides said.

The Senate's Special Committee on Aging, which is also investigating the company's drug pricing practices, said on Wednesday that Shkreli has invoked the U.S. Constitution's Fifth Amendment against self-incrimination, and has refused to produce subpoenaed documents.

Shkreli, 32, fired back at lawmakers on Twitter, writing on Wednesday that the House was "busy whining to healthcare reporters about me appearing for their chit chat next week. Haven't decided yet. Should I?" He declined an interview request.

The outspoken entrepreneur sparked a firestorm last year after he raised the price of Daraprim, a decades-old treatment for a dangerous parasitic infection, to $750 a pill from $13.50 after acquiring it. The medicine once sold for $1 a pill.

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Shkreli pleaded not guilty last month to criminal charges that he ran his companies like a Ponzi scheme, using each subsequent company to pay off defrauded investors from a prior company.

After his arrest, he stepped down as chief executive of Turing Pharmaceuticals and was fired as chief executive of KaloBios Pharmaceuticals Inc. KaloBios also filed for Chapter 11 bankruptcy.

Shkreli's past companies also include Retrophin Inc, which sued him for alleged mismanagement.

Testifying before Congress is risky for someone facing criminal charges because of the chance they could say something prosecutors would later use at a trial. For that reason, many such witnesses invoke the Fifth Amendment and refuse to answer questions.

To even travel to Washington, Shkreli is required to first get the sign-off of a federal judge because his release on bond restricts him to certain parts of New York state. However, judges typically grant temporary travel waivers to white-collar defendants.

U.S. Representative Elijah Cummings of Maryland, the top Democrat on the oversight committee, said the hearing will give Shkreli a chance to explain his views on drug pricing.

"I have been trying for the better part of a year to get information from Martin Shkreli about his outrageous price increases, and he has obstructed our investigation at every turn," Cummings said in a statement.