WASHINGTON — Senate Finance Committee staff members met this month with an Internal Revenue Service whistle-blower who has alleged that senior Treasury Department officials tried to exert influence over the mandatory audit of President Trump’s tax returns, a congressional aide said on Monday.
The whistle-blower contacted the staff of the House Ways and Means Committee over the summer and accused political appointees in the Treasury Department of improperly involving themselves in the audit and putting pressure of some kind on senior officials in the I.R.S.
The Ways and Means Committee has been reviewing the allegations, which were included in a complaint, and in early November the staffs of Senator Charles E. Grassley of Iowa, the Republican chairman of the Finance Committee, and Senator Ron Wyden of Oregon, the panel’s top Democrat, interviewed the I.R.S. employee.
The details of the allegations remain unclear, though a person familiar with the complaint has said that it did not directly implicate Treasury Secretary Steven Mnuchin in the political meddling.
Representatives for Mr. Grassley and Mr. Wyden declined to comment on the meeting with the whistle-blower, citing taxpayer privacy laws.
“We generally do not comment on whistle-blower meetings, their contents or even if they happened,” said Michael Zona, a spokesman for Mr. Grassley. “Additionally, federal law prohibits the discussion of protected taxpayer information.”
Mr. Grassley has been a strong proponent of the rights of whistle-blowers. In September, he introduced bipartisan legislation to extend protections to more people who report violations of securities and commodities laws.
The Washington Post first reported the Senate meeting.
House Democrats have sought to obtain six years’ worth of Mr. Trump’s personal and business tax returns. Mr. Mnuchin has refused a congressional request to release the returns and Mr. Trump has declined to release them, citing a continuing I.R.S. audit.
The review of the whistle-blower’s complaint in the Senate comes as Mr. Trump is locked in a protracted legal battle with Congress over the release of his tax returns. The complaint could potentially buttress the case that House Democrats need access to the tax returns as part of their inquiry into how presidential tax returns are audited.
Two other investigations seeking Mr. Trump’s financial information for other matters are headed to the Supreme Court.
On Monday, Chief Justice John G. Roberts Jr. temporarily blocked an appeals court ruling that required Mr. Trump to turn over financial records to a House committee. The brief order gave no reasons and served to maintain the status quo while the justices decided how to proceed.
Adam Liptak contributed reporting.