Democrats on the House Judiciary Committee sent a letter to White House counsel Don McGahn to urge the Trump administration not to invoke executive privilege to prevent former FBI Director James Comey from testifying before lawmakers next week.

Two Trump administration officials, adviser Kellyanne Conway and press secretary Sean Spicer, would not rule out Friday the possibility of blocking Comey from speaking to the Senate intelligence panel as part of its investigation into Russian meddling in the 2016 election and possible collusion between the Russians and the Trump campaign.

A White House official later confirmed to Bloomberg that the Trump administration is reviewing the matter.

The letter from the Democrats, signed by ranking member John Conyers Jr., D-Mich., and six others, says the use of executive privilege "would be a mistake."

"We write to remind you that any such assertion of privilege is almost certainly baseless, particularly given that Mr. Comey is no longer employed by the Trump Administration," they wrote. "We urge you in the strongest possible terms to counsel the President accordingly. Any assertion of privilege by the President would be seen as an effort to obstruct the truth from both Congress and the American people."

Citing the two types of executive privilege that are applicable under relevant court decisions, the "deliberative process privilege," which could impact governmental decisions and policies and the "presidential communications privilege," the group argues Comey's situation would not apply to either one.

Comey was fired last month amid his agency's probe into possible collusion between the Trump campaign and the Russians. Comey is expected to tell lawmakers on Thursday about his private conversations with Trump. According to a Comey memo reported by the New York Times last month, Trump had asked Comey to lay off his agency's investigation into former national security adviser Mike Flynn. Flynn was fired after it was revealed that he mislead the Trump administration about his communications with a Russian envoy.

One of the letter's signees, Rep. Jerry Nadler, D-N.Y., said Thursday that it would be an "impeachable offense" if Trump fired Comey for refusing to end the Russia investigation.

The letter Friday urges McGahn to avoid a situation in which Trump could be further seen as trying to hide something.

"We caution you that it would fail on the merits. We also warn you that the public would likely — perhaps rightly — view the decision as additional evidence of obstruction of justice," they wrote.