Turing Pharmaceuticals, the company that raised the price of a needed drug by 5,000 percent, is facing a federal probe over antitrust violations, according to reports.

The Federal Trade Commission probe revealed Friday comes a few days after former CEO Martin Shkreli was subpoenaed by Congress to testify as part of a hearing

Reuters cited a letter on the probe to the House Oversight Committee, which subpoenaed Shkreli this week. Shkreli is facing securities fraud charges that don't involve the price hike of Daraprim, an anti-parasite treatment that was jacked up to $750 per pill by Turing last year.

The overnight price hike sparked a public backlash against Turing and Shkreli.

The probe appears to focus on an antitrust investigation that mirrors one by New York's Attorney General, according to Reuters, citing the letter.

The House Oversight Committee isn't the only congressional panel that wants answers from Shkreli.

Sen. Susan Collins, R-Maine, also subpoenaed Shkreli for documents as part of the Senate Special Committee on Aging's investigation into high drug prices.

Collins said on Twitter Wednesday that Shkreli was invoking the Fifth Amendment in response to the subpoena.

"Absent a valid justification for the grounds for invoking the Fifth Amendment, Mr. Shkreli's assertion could hinder our investigation," she tweeted.

Shkreli responded that he still has constitutional rights as a U.S. citizen.

Regarding the subpoena to come before Congress, the panel and Shkreli are battling over whether Shkreli can leave New York to attend the hearing in Washington. Shkreli has said he would plead the Fifth at the hearing.

Turing and the FTC did not immediately return requests for comment.