An outspoken freshman U.S. senator with a record of taking on Wall Street wants financial regulators and federal prosecutors to provide an economic justification for allowing big banks to settle investigations without admitting any wrongdoing.

In a May 14 letter to the heads of the Federal Reserve, the Securities and Exchange Commission and the Justice Department, Massachusetts Democratic Senator Elizabeth Warren asks the agencies to provide her with details of how they weigh the costs and benefits of settling versus trying cases.

“If a regulator reveals itself to be unwilling to take large financial institutions all the way to trial—either because it is too timid or because it lacks resources—the regulator has a lot less leverage in settlement negotiations and will be forced to settle on terms that are much more favorable to the wrongdoer,” Warren wrote.

Concerns about whether regulators are properly weighing the costs and benefits of their policies have typically been voiced by Republicans and the financial industry as a defense against regulations they oppose.

Allegations of conducting a shoddy cost-benefit analysis have been used successfully by corporate groups in legal challenges to SEC rules.

They have also arguably led to a slowdown by financial regulators as they try to finalize provisions required by the Dodd-Frank Wall Street reform law.

The use of the argument by Warren marks a rare occasion in which a liberal has adopted the same strategy, but this time to promote a pro-regulatory agenda.

“Have you conducted any internal research or analysis on trade-offs to the public between settling an enforcement action without admission of guilt and going forward with litigation as necessary to obtain such admission?” Warren asks in her letter.

Both the SEC and the Justice Department have faced criticism for the handling of cases tied to the 2007-2009 financial crisis.

The bulk of the criticism against the DOJ has centered on the fact that it has not brought many actions against Wall Street banks and that few high-level executives have gone to jail.

In instances where they do settle criminal allegations, however, the DOJ does usually require the admission of certain facts.

The SEC, by contrast, has brought the most financial crisis cases of any government agency. However, in many of those cases, the SEC has allowed banks to settle the civil charges without admitting or denying the allegations.

The SEC’s settlements have been challenged by Federal District Court Judge Jed Rakoff, who refused to approve a proposed $285 million settlement with Citigroup Inc. in connection with a financial crisis case.

The SEC and Citigroup have appealed that decision and are awaiting a ruling.

Previously, Rakoff also turned down a $33 million SEC settlement with Bank of America Corp., and only approved it after the amount was raised to $150 million.

Warren first raised concerns about whether banks were “too big for trial” in her debut Senate Banking Committee hearing in February.

In that hearing, she sharply questioned top officials from the Office of the Comptroller of the Currency and the SEC, among others, about the last time they took a big Wall Street bank to trial.

The video of her exchange later went viral on the Internet and inspired a liberal political action committee to launch an online petition urging the SEC to take more banks to trial.

After the hearing, Warren also sent a letter to Comptroller of the Currency Thomas Curry asking him the same question she is now asking the SEC, DOJ and Fed—has an internal analysis weighing settlements with admissions versus trials been done?

Warren said the OCC later told her no such analysis existed.

A spokeswoman for the Federal Reserve declined to comment on Warren’s letter.

Spokesmen for the SEC and the Justice Department had no immediate comment.