WASHINGTON ― Republicans in Congress have formally asked Democrats to stop trying to get their hands on President Donald Trump’s tax returns.

Democrats are holding a hearing Thursday on the importance of disclosing Trump’s tax information, which would reveal how much money he makes, who pays him and how much tax he pays.

Top-ranking Republicans on the House tax committee asked its chairman not to request the documents, even though federal law explicitly gives him the power to do so ― and even though Republicans used that power to oversee Barack Obama’s administration.

“Transparency in our government is enormously important, but must be undertaken with appropriate care,” Reps. Kevin Brady (R-Texas) and Mike Kelly (R-Pa.) wrote in a Thursday letter to Ways and Means Committee Chairman Richard Neal (D-Mass.).

“Weaponizing our nation’s tax code by targeting political foes only serves to weaken our system of government, not strengthen it,” Brady and Kelly wrote. “If there are valid concerns with financial disclosure, then let’s come together to legislate a thoughtful solution to require additional disclosures.”

Trump broke with precedent of the last 40 years by refusing to release his tax returns during the 2016 presidential campaign. And he broke with tradition when he took office without divesting from his businesses.

It’s normal for congressional committees to conduct oversight of the executive branch, but Trump said during his State of the Union address on Tuesday that Democrats should lay off.

“If there is going to be peace and legislation, there cannot be war and investigation,” Trump said.

Ways and Means can obtain anyone’s tax returns under a provision of the tax code. This provision has existed since the 1920s, when Congress enabled three congressional committees to obtain the president’s tax returns without the chief executive’s consent. Those committees can then release those tax returns to the full House or Senate if they choose. The Joint Committee on Taxation famously did so in 1974 when it sent its report on President Richard Nixon’s tax returns to the House.

In 2014, Republicans on the Ways and Means Committee used their authority under the same provision to obtain the tax information of several private groups that were seeking nonprofit status from the IRS. They then voted to release that information publicly in a letter that sought criminal prosecution of a former IRS official for allegedly targeting conservative groups for audits.

Brady and Kelly were members of Ways and Means in 2014, as were several other Republicans currently on the committee.

At the hearing, a panel of four expert witnesses testified that the committee has broad authority to request tax returns from the president or anyone else. But Republicans argued the committee had no need to obtain Trump’s returns because the IRS is mandated to audit them and the president already has to make other financial disclosures.

The witnesses, however, argued that Congress sought Nixon’s tax returns because they did not trust the IRS to properly audit the president’s taxes without undue influence, and because tax returns contain different information than what’s required by mandatory financial disclosures.

Representatives for Treasury Secretary Steve Mnuchin have said he would review any requests “for legality,” suggesting the Trump administration would defy Congress ― and defy the law.

“I don’t see any wiggle room in the statute for the secretary to refuse a request,” George Yin, a tax expert at the University of Virginia Law School, testified.

This story has been updated with details from Thursday’s hearing.