Nine senators are pushing U.S. Attorney General Jeff Sessions to reveal what he knows about a reported investigation into Health and Human Services Secretary Tom Price’s stock trades that a top federal prosecutor might have begun before being fired by the Trump administration this month.

In a letter Wednesday, seven senators — six Democrats plus Vermont independent Bernie Sanders — called on Sessions to assure them that any investigation of Price — or others connected to the Trump administration — would be “allowed to continue unimpeded.” Three Democratic senators sent a different letter a day earlier, asking Sessions to “provide greater clarity” about why Manhattan’s former U.S. attorney, Preet Bharara, was fired and whether any investigation of Price was a factor in Bharara’s removal.

ProPublica, a nonprofit news organization, reported March 17 that Price was being investigated by the U.S. attorney’s office for his stock trades, though it did not specify which trades Bharara was investigating before his dismissal. The website attributed its report to an unnamed person familiar with the U.S. attorney’s office, and neither the Justice Department nor other news media organizations have confirmed its existence.

If an investigation had begun, it would be hard to derail. But investigations of federal officials are always sensitive cases, said Donald Langevoort, a securities law professor at Georgetown University.

“The higher up the food chain you go, the more prominent the person is, the more confident you better be that you have the evidence you can present to a jury,” he said. “But I think any attempt to quash an investigation would backfire considerably.”

Price, a prominent Republican congressman until he joined President Donald Trump’s Cabinet this year, was questioned extensively at his confirmation hearings about stock purchases he made in health care, pharmaceutical and medical device companies while serving on the House of Representatives’ health subcommittee.

The activity raised conflict-of-interest concerns for some members of Congress because Price’s trades overlapped with his sponsorship of bills, advocacy or votes on issues related to those companies or their industries.

The Democrats  called attention to Price’s investment in a small Australian biotech firm, Innate Immunotherapeutics, which Price testified he learned about from another congressman, Rep. Chris Collins (R-N.Y.), Innate’s largest shareholder.

Price bought most of his shares at discounted prices in two private stock placements in 2016 offered to a small number of sophisticated investors — many with personal or professional ties to Collins.

Congressional Democrats slammed Price at his hearings for buying shares at advantageous prices not available to all investors. Some questioned whether Price had violated insider trading laws or the Stop Trading on Congressional Knowledge (STOCK) Act, which bans members of Congress from trading on stocks using information they received in carrying out their official duties.

“Despite the many unanswered questions that remained, Republicans rushed Price’s nomination through the Senate without waiting for answers,” seven senators said in Wednesday’s letter.

When he was confirmed Feb. 10, Price agreed to divest his stock holdings within 90 days of  taking his post. An HHS spokesperson said Price has completed those divestitures but declined to provide further information.

Sen. Elizabeth Warren (D-Mass.) was the only senator who signed both letters to Sessions.

Other names on Wednesday’s letter were Patty Murray (D-Wash.), Ron Wyden (D-Ore.), Bernie Sanders (I-Vt.), Al Franken (D-Minn.), Tammy Baldwin (D-Wis.) and Maggie Hassan (D-N.H.).

Tuesday’s letter was also signed by Richard Blumenthal (D-Conn.) and Jeff Merkley (D-Ore.).

Sessions’ office confirmed it had received Tuesday’s letter from the senators but declined to comment on either one. The U.S. Attorney’s Office in Manhattan also had no comment.