Sen. Elizabeth Warren, the Massachusetts politician and 2020 hopeful, on Tuesday pressed Federal Reserve Chairman Jerome Powell on the regulator’s high percentage of approvals for bank mergers and acquisitions.

How high? One-hundred percent.

In a heated line of questioning in his testimony to the Senate Banking Committee on Tuesday, Warren noted that among the 3,819 applications for bank mergers received by the Fed since 2006, none were rejected. Asked if “zero sounds right,” Powell responded, “if you say so.”

It was an unusually barbed exchange for Powell, who has tried to build a cordial rapport with Congress by working the halls of Capitol Hill. Reuters reported that Powell has interacted with at least 72 members of Congress between February and November of last year.

Warren asked the question amid concerns over the pending merger between BB&T (BBT) and SunTrust (STI), which would create the sixth largest U.S. bank if approved by the Fed. That entity would be magnitudes smaller than the big four banks.

She took particular issue with the timing of the Fed’s approval process. Banks seeking to merge often consult with their regulators before officially announcing anything, and Warren argues that these discussions effectively allow regulators like the Fed to “grease the wheels” before it’s made public. Warren said that this disadvantages communities that could be negatively impacted by the deal since they only have the opportunity to protest after it’s announced, by which point regulators may have already given the banks the green light to merge.

“No wonder you’ve approved 100% of the merger applications,” Warren said. “Not a single ‘no.’ Your approval process itself appears to be a rubber stamp, that everything is happening behind closed doors.”

With only a few chances to respond, Powell insisted that the Fed is “going to conduct a very fair and open transparent process” with regard to any application it receives.

Powell also said that bank mergers facing a “statutory problem” may withdraw their applications upon realizing that they may not survive the approval process, meaning the Fed would never have an opportunity to formally deny the application. Warren acknowledged this point and noted that about 13% of the 3,819 applications in question were withdrawn.

Community input

Warren actually began her inquiry on the Fed’s merger process immediately after the BB&T-SunTrust deal was announced in early February. She asked the Fed for detail on how regulators assess the impact of a merger on a community when it reviews that merger’s application. Citing Yahoo Finance reporting, Warren expressed concern that the possible wave of large bank consolidation could “result in reduced competition and choice for consumers and small businesses.” In some mergers, management chooses to close branches and lay off employees in order to achieve cost saves.