House Republicans investigating the liberal fund-raising organization ActBlue have asked its chief executive to testify next month to explain how the group vets its donors, a significant escalation in public pressure on the Democratic Party’s biggest financial engine.

In a letter on Thursday, Representative Bryan Steil of Wisconsin, the chairman of the House Administration committee, asked Regina Wallace-Jones, the ActBlue chief executive, to appear at a public hearing on May 19 to answer questions about the organization’s fraud prevention efforts.

The move follows reporting in The New York Times this month revealing that lawyers for ActBlue had warned the organization that it might have misled Congress in a 2023 letter. That letter was a response to a request by Mr. Steil for information about how ActBlue vetted donations from other countries. People who are not United States citizens or permanent residents are prohibited from donating directly to federal candidates or political action committees.

In Mr. Steil’s request on Thursday for Ms. Wallace-Jones to appear, he alluded to the Times article and some of the internal ActBlue documents it mentioned. He suggested that the organization had not provided all the documents it should have offered in response to a subpoena last year.

Mr. Steil wrote that there were “outstanding questions” about “whether and how” ActBlue had remedied its approach to fraud prevention.

Ms. Wallace-Jones and ActBlue have denied doing anything wrong. ActBlue did not immediately respond to a request for comment on Thursday.

President Trump and congressional Republicans have long pushed to investigate ActBlue in an apparent effort to undermine the Democratic Party’s main fund-raising vehicle, which powers the party’s candidates up and down the ballot.

The House Administration committee began its inquiry into ActBlue in 2023, and was joined last year by the House Judiciary and Oversight committees in the investigation.

ActBlue and other Democrats have denounced the Republican efforts as a political witch hunt and have noted that Republicans have not made similar inquiries into WinRed, the primary payment processor for G.O.P. candidates.

House Republicans’ request on Thursday for Ms. Wallace-Jones follows a demand they made last week that ActBlue produce a host of documents. In that letter, the chairmen of the three committees suggested that the organization had obstructed their investigation, “including through misleading statements and noncompliance with our subpoenas.”

The letter gave ActBlue until April 28 to produce the documents.

The Times article this month detailed how, in February 2025, ActBlue was warned by the law firm Covington & Burling that a 2023 letter signed by Ms. Wallace-Jones and sent to Mr. Steil’s committee had created “a substantial risk for ActBlue.” Parts of the letter that described ActBlue’s vetting process for foreign donations were not necessarily correct, Covington wrote.

Covington did not identify any specific illegal contributions, and it suggested that the scope of any potential problems was unclear. Kimberly Peeler-Allen, the chairwoman of the ActBlue board of directors, said in an interview for the earlier Times article that “less than 1 percent” of contributions from the 2024 election cycle had signs that they were from foreign countries.

The Covington memos prompted a string of resignations from ActBlue, including members of its legal and compliance departments.