WASHINGTON (CN) – A House oversight subcommittee made initial forays Thursday into obtaining the tax returns of presidents and presidential candidates by reviewing legislation that would require such disclosure, spurring Republicans to push back against Democratic calls for transparency.

The proposed measure, energized by a newly Democratic-controlled House, is part of the wide-reaching House Resolution 1 election reform bill.

Expert witnesses at Thursday’s House Ways and Means Oversight Subcommittee hearing were questioned by lawmakers over the extent to which current U.S. tax law allows the committee to get tax documents from executive branch officials and future candidates.

Incoming presidents are currently required to fill out financial disclosure forms and be audited by the IRS, but there is no law that requires they disclose their income taxes. Presidents in the past have willingly provided those documents upon assuming office, a tradition that President Donald Trump departed from.

“What we’re talking about here is an informal tradition, it’s not law,” Representative Jackie Walorski, R-Ind., said, echoing a sentiment that would be repeated on the GOP side of the aisle. “This is all about weaponizing our tax laws to target a political foe. Doing this, I believe, sets a dangerous precedent.”

Republicans argued that for the Ways and Means Committee to draw authority from the tax code to obtain Trump’s tax records would be a slippery slope that could compromise the privacy of private citizens.

“Such an abuse of power would open up Pandora’s Box. It would be tough to get the lid back on,” said GOP ranking member Mike Kelly of Pennsylvania. “Where does it end? What about the tax returns of the speaker? Members of Congress? Federal employees? Or for that matter, any political donors?”

Trusting that the IRS is doing its job auditing Trump, and the fact that disclosing tax returns has never been required by law, Republicans pushed back against Democrats’ call for transparency. Some suggested amending the financial disclosure forms to require more information as an alternative to a carte blanche requirement to disclose tax filings.

Making Trump’s personal finances public record could, Democrats argue, reveal who the president could still be beholden to financially, as well as whether he benefited from his own tax cuts passed in 2017.

Like the two-term presidency requirement – which was simply a gentleman’s agreement before President Franklin Delano Roosevelt was elected to a fourth term in 1944 – some “matters of custom and practice” that aren’t necessarily law need to be officially enforced, according to California Democrat Jimmy Gomez.

“Oftentimes somebody comes along and rips apart a custom within the body politic. The legislative branch or the republic itself has to take action to codify that custom and practice,” Gomez said.

Subcommittee Chairman John Lewis, D-Ga., ended by reiterating that the American people have a right to know Trump’s financial entanglements.

“This hearing is not the end” of deliberations he said, but just the beginning.

“We’re moving along in a diligent way and a very deliberate way and we’re going to get the answers,” Representative Bill Pascrell, D-N.J., told reporters after the hearing. “We can’t rush into this thing. It’s very complex.”