Elizabeth Warren’s long-simmering feud with billionaire investor Leon Cooperman may soon lead to a contentious Capitol Hill face-off.

Senator Warren, Wall Street’s most vocal critic in Congress, has asked Cooperman to testify at an April 27 hearing on taxes. The request follows years of tit for tats between the two, with Warren ripping Cooperman for opposing levies on the mega-rich and him accusing her of unfairly vilifying the wealthy.

Warren, a Massachusetts Democrat who’s chair of the Senate Finance Committee’s Subcommittee on Fiscal Responsibility and Economic Growth, asked Cooperman to confirm by April 22 whether he will appear. The hearing is focused on “creating opportunity through a fairer tax system,” according to a letter her office released Tuesday.

“I am particularly interested in providing you with an opportunity to discuss my Ultra-Millionaire Tax Act, which would level the economic playing field and narrow the racial wealth gap,” she wrote.

CNBC, which was first to report on the invitation, subsequently reported that Cooperman, 77, is considering the request, but questioned whether it was genuine.

“I’m trying to determine whether she’s being objective or whether she’s just trying to promote her own agenda,” the network quoted Cooperman as saying, citing a call with him while he was on a boat fishing. “I’m a bit suspicious given how she never responded to the letter I sent her before.”

He famously wrote to Warren in October 2019 when she was in the midst of a failed run for the White House, arguing that the lawmaker ignored all the ways that the wealthy benefit society, particularly through charitable giving. Cooperman, who grew up in the South Bronx and is the son of an immigrant plumber, didn’t immediately respond to requests for comment from Bloomberg.

Warren has said her tax proposal would raise at least $3 trillion in revenue over a decade by requiring the wealthiest 100,000 households, or the top 0.05%, to pay more. Tax levels for the rest of American households would be unchanged.

Cooperman, who stopped managing client money in 2018, has countered that her plan is “foolish,” lacks merit, may be illegal and has little chance of becoming law. Warren referenced those criticisms in her letter, which was dated Monday. She said that a formal invitation from Senate Finance Committee Chairman Ron Wyden, an Oregon Democrat, would follow if Cooperman agrees to her request.

With assistance from Hema Parmar.

This article was provided by Bloomberg News.