Federal Reserve chair Janet Yellen said on Thursday she was open to raising a threshold for determining a bank’s systemic importance and indicated that US lenders had made progress in their submissions of so-called living will plans this month.

The tacit nod of approval from the Fed chief is a good sign for Wall Street, as a rejection can be costly, though Yellen also made clear the US central bank will not hesitate to reject certain plans when it completes its assessment.

“We are certainly prepared to say that they are not credible,” Yellen told the Senate Banking Committee during the second and final day of her semiannual testimony to Congress on the economy and monetary policy.

The questions aimed at Yellen focussed more on financial industry regulation than the timing of an interest rate hike.

One topic that emerged was the threshold for so-called SIFIs.

The 2010 Dodd-Frank financial reform law says that all US banks with more than $50 billion in assets are labelled systemically important financial institutions (SIFIs), making them subject to tougher supervision by the central bank.

A bill drafted by Republican Richard Shelby, the committee chairman, and passed by the panel in May proposes allowing banks with assets between $50 billion and $500 billion to lose the SIFI designation if the Fed believes they are not systemically risky.

“I would be open to a modest increase in the threshold,” Yellen said.

She added that it is critical for the Fed to maintain its discretion over systemically important banks should the SIFI threshold change.