An FEC commissioner repeated her demand Tuesday that the White House provide proof for its claims that thousands of people were bused from Massachusetts into New Hampshire to vote illegally in the 2016 election. She also defied a letter from a Koch brothers-funded group that asked that she be investigated for her actions.

The commissioner made a similar demand for proof last week.

The statement cites a group funded by the Koch brothers, Cause of Action, which sent a letter Tuesday to the inspector general of the FEC, requesting an investigation into what it claimed was Weintraub overstepping her authority as a commissioner.

The commissioner, Cause for Action claimed, “violated applicable ethics regulations when she used government property and official time to call on President Trump to provide evidence of his claims of voter fraud in New Hampshire and then continued to promote her statement after it was issued.”

Here’s the “request for investigation” that a nonprofit filed today with @FEC Inspector Gen., seeking to muzzle me. https://t.co/BcqygrE4ii — Ellen L Weintraub (@EllenLWeintraub) February 21, 2017

“The President of the United States has, without providing evidence, alleged a massive conspiracy to bus thousands of voters from one state to another to cast illegal votes in the 2016 elections,” commissioner Ellen Weintraub wrote in a statement posted online Tuesday.

“Any such allegation challenging the legitimacy of federal elections would be of great concern to me,” Weintraub continued. “As it happens, this particular allegation falls squarely within the jurisdiction of the Federal Election Commission, since the expense of these buses has not been accounted for on any campaign-finance filing. Accordingly, I have asked the President for his evidence.”

On Feb. 9, Trump reportedly told a closed-door meeting of senators that “thousands” of people who were “brought in on buses” from Massachusetts voted illegally in New Hampshire, costing him the state’s electoral votes, and former Sen. Kelly Ayotte (R-NH) her job.

Trump reportedly provided no proof for his claim, and neither did his senior policy adviser Stephen Miller, when he repeated the claim during an interview with ABC’s “This Week.”

“But let there be no doubt: It is absolutely within my official duties as a federal election official to comment publicly on any aspect of the integrity of federal elections in the United States,” Weintraub concluded. “I will not be silenced.”

Weintraub, a Democrat, was first appointed to the FEC by George W. Bush in 2002. The commission has been plagued by obstruction for years: no more than three of its six members can be of the same party, while four members must agree to begin an investigation.

This article has been updated.