Democrats, who disclosed the existence of the whistleblower as part of their lawsuit seeking President Donald Trump’s tax returns, have been vague about what the person is alleging, beyond that someone in the administration may have tried to interfere with an audit of either Trump’s or Vice President Mike Pence’s tax return. Those audits are automatic for sitting presidents and vice presidents.

In a court filing, Democrats said they were first approached in July by a federal employee “setting forth credible allegations of ‘evidence of possible misconduct’ — specifically, potential ‘inappropriate efforts to influence’ the mandatory audit program.” They did not offer additional details, though lawyers for the House said they could tell the judge more in private.

The Washington Post reported that in his complaint, the whistleblower said he was told that at least one Treasury official had attempted to improperly influence the IRS examination. The person declined to discuss specifics in an interview with the Post.