WASHINGTON ― Rep. Maxine Waters (D-Calif.) sent a sharply worded letter to Attorney General Loretta Lynch on Friday, calling on the government’s top lawyer to rescind a drug money laundering settlement with HSBC and bring criminal charges against the British financial titan’s employees.

Under the standards of Beltway etiquette, it’s a provocative move for a Democratic congresswoman in a leadership position ― Waters is the ranking member of the powerful House Financial Services Committee ― to publicly challenge a sitting Democratic cabinet member. But Waters’ letter is particularly biting for another reason: Lynch was personally in charge of the HSBC investigation that infuriated financial reform advocates in December 2012, while she was U.S. Attorney for the Eastern District of New York.

“I have long criticized the apparent two-tiered American justice system that subjects low-level criminal offenders to harsh prison sentences that completely upend their lives and compromise their futures, while allowing the perpetrators of major financial crimes to be largely shielded from criminal prosecution,” Waters wrote Friday.

The HSBC deal, known technically as a deferred prosecution agreement or DPA, settled charges that the company laundered $881 million for the Sinaloa and Norte del Valle drug cartels and violated U.S. government sanctions against Iran, Libya, Sudan and other countries. The bank paid the feds $1.9 billion and no bankers were prosecuted. Waters wasn’t happy at the time, and needled then-Attorney General Eric Holder about the deal in 2013.

But roughly two years after Lynch finalized the deal, reports surfaced showing that an HSBC whistleblower had turned over information to the DOJ suggesting that the firm’s Swiss unit had engaged in massive tax evasion efforts. The documents reached the department during Lynch’s money laundering investigation, which never mentioned anything about tax evasion; Lynch said her office never saw the documents.

This year, Lynch’s money laundering settlement suffered further embarrassment after the official appointed to monitor HSBC’s money laundering reforms reported that the company still isn’t up to snuff.

“More than halfway into a five-year DPA that is set to end next year, HSBC’s compliance program is still ineffective at catching and stopping federal banking law violations,” Waters wrote to Lynch. “This is unacceptable.”

HSBC was in congressional crosshairs last week when House Financial Services Committee Chairman Jeb Hensarling (R-Texas) published a 282-page report on the HSBC settlement, alleging that Holder had personally insisted on not prosecuting bankers, arguing that doing so would jeopardize the global financial system. Hensarling and Waters are typically partisan enemies and ideological opponents. He wants to dismantle the 2010 Dodd-Frank financial reform law, while Waters wants to strengthen it. But on the “too big to jail” problem at least, Waters apparently sees no need to distance herself from her typical foe.

“I implore you to revisit and reconsider HSBC’s DPA,” Waters wrote, “and to pursue the prosecution of the HSBC employees that have thus far avoided facing justice.”