Federal Reserve Chairwoman Janet Yellen indicated Wednesday that she is open to the idea of changing the definition of a bank subject to tighter regulation, giving some ammunition to Republicans seeking to ease the regulatory burden of the law on some banks.

In a Senate hearing Wednesday afternoon, Yellen said that she "would be open to a modest increase in the threshold" used to define big banks under the 2010 Dodd-Frank financial reform law. Currently, that threshold is $50 billion in assets, low enough to capture some regional banks that lawmakers have argued are not the systemic threat that Wall Street banks with trillions of dollars in assets are.

"What we've found is that, in some cases, the burden associated with that for many of those firms really exceeds the benefit to systemic stability," Yellen said, citing specifically the difficulty of banks in complying with the stress tests regulators put them through.

Republicans on the Senate Banking Committee have voted for far-reaching legislation that would get rid of the $50 billion threshold in favor of having regulators determine which banks needed added supervision case-by-case.

The bill, however, received no Democratic support and is not likely to clear the Senate. Yet a number of Democrats, including the ranking member of the panel, Sen. Sherrod Brown of Ohio, favor raising the threshold to provide relief to regional banks.

Federal Reserve Governor Daniel Tarullo, the agency's point man on regulatory issues, endorsed raising the threshold to $100 billion in a Senate hearing last year.

Without citing a specific number, Yellen said that she would be open to raising the limit, cautioning that it would be "essential" for the Fed to retain its ability to add additional requirements for banks that might fall below the asset threshold but still pose potential risks to the financial system.

The asset threshold was the subject of debate among senators at Thursday's hearing.

Sen. Elizabeth Warren, D-Mass., issued a warning against changing it, saying that to do so would be to "cut loose about 30 or so of the biggest banks in this country and just hope for the best. If it doesn't work out, the taxpayers can pick up the tab again."

"The other approach is to play it safe, keep the threshold where it is and allow the Fed to tailor the rules to fit the risks posed by these different banks," said Warren, a vocal critic of Wall Street practices and its influence in Washington.