ActBlue, the Democratic online fundraising platform, is firing back at a GOP-led congressional investigation, accusing lawmakers of violating their constitutional rights, Politico reported on Monday.

President Donald Trump has issued executive actions targeting the platform, which for years has served as the backbone of grassroots fundraising for Democratic candidates around the country, under the assertion that the platform is allowing fraudulent foreign contributors to interfere in U.S. elections. GOP lawmakers are investigating along similar lines — but attorneys representing ActBlue have cried foul that the whole thing is a ploy to find evidence for a criminal investigation, according to their new letter sent to Reps. Jim Jordan (R-OH), James Comer (R-KY), and Bryan Steil (R-WI).

"ActBlue has been cooperating with the Committees’ investigations for almost a year and a half," said the letter, citing thousands of pages of document productions to House investigators. "We are concerned, however, by recent public actions that suggest that the Committees’ investigation is not an exercise of legitimate legislative oversight, but rather has become a partisan effort to exploit legislative processes to gather information in service of a White House-directed Justice Department investigation."

"The Committees have announced that they intend to use the Committees’ ongoing work to advance a purported Department of Justice investigation of ActBlue ordered by the President," the letter continued. "Doing so would be inconsistent with the previously stated purpose of the Committees’ investigation. Bedrock constitutional protections and Supreme Court precedents prohibit Congress from serving as an investigative arm of the Executive Branch."

ActBlue's attorneys demanded more information about the committees' contacts with the Justice Department in order to continue moving forward cooperating with the investigation.

All of this comes at a tumultuous time for the organization, which has seen a departure of more than half a dozen senior staff this year.