White House counsel Pat Cipollone sent a letter to Rep. Elijah Cummings (D-Md.), the committee chairman, saying senior White House advisers are “absolutely immune” from congressional testimony and are allowed to refuse to appear before a congressional committee.

The White House said Monday that it refuses to allow presidential counselor Kellyanne Conway to testify at a House Oversight Committee hearing about several alleged Hatch Act violations.

The refusal may bring a subpoena from the committee, which is reviewing Conway’s potential violations of the federal law prohibiting government employees from engaging in partisan political activity. The committee had scheduled the hearing for Wednesday with the U.S. Office of Special Counsel (OSC), which is unrelated to former special counsel Robert Mueller’s office.

The OSC, an independent federal agency, sent a report to President Donald Trump earlier this month outlining several occasions in which Conway violated the Hatch Act by bashing Democratic presidential candidates in her official capacity to groups of reporters, on national television and in social media. In her first Hatch Act violation in 2017, Conway boosted Ivanka Trump’s commercial products during an interview on cable TV.

The agency recommended Trump fire Conway, though the president refused to remove her from his staff. His defense of her followed a White House statement accusing the OSC of trying to “weaponize” the Hatch Act and violate Conway’s “constitutional rights.”

Neither Trump nor Conway has denied that the presidential aide violated the Hatch Act. The president has indicated the law itself is unconstitutional, though the Supreme Court has upheld it twice in 80 years.

The OSC Special Counsel Henry Kerner slammed the White House in a June 13 letter to Trump, saying that Conway’s violations “if left unpunished, send a message to all federal employees that they need not abide by the Hatch Act’s restrictions. Her actions erode the principal foundation of our democratic system ― the rule of law.”