The leaders of the Senate Intelligence Committee on Tuesday announced that they were issuing two additional subpoenas for businesses associated with former national security adviser Michael Flynn.

The subpoenas — focused on a pair of businesses in Alexandria, Va., associated with Flynn — were among the panel’s first slate of responses to Flynn’s refusal to respond to a subpoena for documents related to the committee’s probe into Russian election meddling.

Sens. Richard Burr (R-N.C.) and Mark Warner (D-Va.), the chairman and vice chairman, respectively, have also sent a letter to Flynn’s attorney challenging whether he can legally claim Fifth Amendment protections to a request for documents.

Flynn on Monday refused the committee’s initial subpoena for documents, claiming the Fifth Amendment right against self-incrimination and citing the “escalating public frenzy” surrounding the request.

{mosads}“The context in which the Committee has called for General Flynn’s testimonial production of documents makes it clear that he has more than a reasonable apprehension that any testimony he provides could be used against him,” Flynn’s lawyers wrote in a letter to Burr and Warner.

Corporations are not subject to Fifth Amendment protections, providing committee leaders with an alternative avenue to obtain the information they want.

“While we disagree with Gen. Flynn’s lawyer’s interpretation of taking the Fifth, it is even more clear that a business does not have a right to take the Fifth if it is a corporation,” Warner said.

Flynn for months has said he would testify before Congress only if granted immunity, a deal lawmakers have shied away from making to avoid interference with the separate, federal probe into Russian interference in the election.

Committee leaders now must decide how far to go in enforcing the congressional subpoenas.

If they do seek to enforce the orders, they will need the support of the full Senate and the cooperation of the Justice Department.

For now, it’s unclear how much appetite the Senate panel has to hold Flynn in contempt of Congress — the first step to enforcing the subpoena.

“We’ve taken the actions we feel are appropriate right now. If there is not a response, we will seek additional counsel advice on how to proceed forward. At the end of that option is a contempt charge,” Burr told reporters Tuesday. “I’ve said everything is on the table.”

But, he added, “That’s not our preference.”

Congressional investigations have a longstanding history of coordinating with any simultaneous federal probes to avoid inadvertently damaging the Justice Department’s ability to levy prosecutions in a given case.

In Flynn’s case, the committee has taken a grant of immunity off the table completely.

“It’s a decision that the committee has made that we’re not the appropriate avenue in a potential criminal investigation,” Burr said Tuesday. “As valuable as Gen. Flynn might be to our counterintelligence investigation, we don’t believe it’s our place today to offer him immunity.”

The federal probe into Flynn appears to be escalating. The U.S. Attorney’s office in Northern Virginia reportedly issued its own subpoenas for records related to Flynn’s business dealings earlier this month.

The appointment of a special counsel, former FBI Director Robert Mueller, may also remove some of the pressure on Senate leaders to go after Flynn too aggressively. The move, intended to remove the specter of political interference in the investigation, was met with widespread support on Capitol Hill.

Flynn, who was ousted in February for misleading Vice President Pence about the contents of interactions with the Russian ambassador to the U.S., has been a point of fierce scrutiny in the various investigations into election meddling.

The former intelligence official took tens of thousands of dollars in payments from the Russian state-backed network RT and failed to tell the government when he reapplied for his security clearance.

Trump has continued to back Flynn. He has previously applauded Flynn’s demands for immunity, citing a “witch hunt” against him.