A top member of the Senate Finance Committee is urging the FBI to refuse to cooperate with a congressional Ukraine investigation.

Sen. Ron Wyden of Oregon, the top Democrat on the committee, on Thursday morning sent a letter to FBI Director Chris Wray and Attorney General Bill Barr urging them to stiff-arm a request from two Senate chairmen for materials from Alexandra Chalupa, a former Democratic National Committee consultant. The Daily Beast obtained the letter.

Chuck Grassley and Ron Johnson, the Republican chairs of the Senate Finance Committee and the Senate Homeland Security and Governmental Affairs Committee, asked Wray late last year to turn over the FBI’s images of Chalupa’s phone and computer. Chalupa has said she voluntarily provided those devices to the FBI after she was the victim of what appeared to be a Russian government-sponsored hack. The FBI made digital copies of the phone and laptop’s contents, a standard step in cyber crime investigations.

And now Grassley and Johnson want those records.

In November, they asked Wray to turn over the materials for their own investigation into allegations that the Ukrainian government colluded with the DNC to damage the Trump campaign. In their investigation, Chalupa isn’t a victim; she’s a potential villain. Intelligence Community officials, meanwhile, have reportedly briefed Congress that Russian security services are pushing allegations regarding Ukraine and collusion as part of a disinformation campaign. And Fiona Hill, a former top Russia official on Trump’s National Security Council, said the allegations are fiction.

That’s why Wyden is taking the atypical step of urging the executive branch not to cooperate with a request for materials. In the letter, he argued FBI cooperation would discourage future victims from sharing evidence with the bureau.

“The Senators’ request will have a chilling effect on the victims of nation-state cyber-attacks,” he wrote, “and would discourage them from seeking law enforcement assistance, thereby jeopardizing our national security, limiting our ability to respond to sophisticated cyber-attacks, and undermining the civil liberties of American citizens.”

Wyden also called the Ukraine probe “an effort to legitimize Russian propaganda.”

“The FBI is not a political weapon,” he wrote, “and should not be pressured into violating a citizen’s civil liberties for political gain.”

In a statement to The Daily Beast, a Grassley aide wrote, “It’s disappointing that Sen. Wyden has decided to ignore legitimate questions about election security and instead regurgitate misleading liberal talking points to quash scrutiny of reported election tampering by a Democratic political operative. Wyden’s letter conflates Russian propaganda efforts with unrelated reports of potential election interference that have yet to be fully investigated. In fact, Senators Grassley, Johnson and Graham clearly state that their inquiry is ‘unrelated to an uncorroborated theory that Ukraine was also behind the hack of DNC servers.’ Despite his complaints, Wyden neglected to mention that subjects of the inquiry have already voluntarily provided Congress with records Wyden argues should not be sought. With another election less than 10 months away, it’s a shame that the Democrats would choose to interfere with an ongoing investigation into potential election vulnerabilities instead of joining it.”