Senator Elizabeth Warren has formally requested Treasury Secretary Scott Bessent to justify the Trump administration's decision to intervene in the Japanese yen market, continuing the veteran Democrat's scrutiny of the administration's foreign exchange policies.

In a letter dated August 13, Warren wrote: "To date, the administration has not provided a detailed rationale for the intervention, nor has it formally disclosed how much taxpayer money was used to purchase yen."

Bessent has previously confirmed media reports of a joint U.S.-Japan intervention to support the yen, the first such collaboration since 1998. The operation occurred on July 31, but he has yet to specify the exact amount of funds deployed. He did reveal that the action utilized euro holdings from the Treasury's Exchange Stabilization Fund (ESF).

Warren noted that Congress requires the ESF's authority to be "used cautiously to advance the national interest." She demanded that Bessent provide "a legal analysis of the use of the Exchange Stabilization Fund" and requested a response from the Treasury Department by August 28.

As the ranking Democrat on the Senate Banking Committee, Warren also asked Bessent to estimate the cost of the operation to U.S. taxpayers and to detail "the size and conditions of any U.S. financial support currently being considered for Japan."

Warren further inquired more broadly about how turmoil in Japanese financial markets could potentially impact U.S. employment, wages, and financial stability.

Japan is the largest foreign holder of U.S. Treasury bonds. Analysts speculate that one reason Bessent decided to intervene in the yen was to prevent Tokyo from selling its U.S. debt holdings, as a large-scale sell-off could push up U.S. bond yields.

Bessent's Previous Use of the ESF to Support Argentina

Bessent previously used the ESF to intervene in the Argentine peso in the fall of 2025, providing support to President Javier Milei's government.

Warren had also called for a review of that action at the time. In her latest letter, she referred to the operation as "a politically motivated, taxpayer-funded bailout."

Bessent has stated that the U.S. actually profited from its support of Argentina, but the Treasury has not released specific details about that intervention.

Questions Over the Use of Euro Reserves

Warren also asked whether the Treasury consulted with the European Central Bank (ECB) before using euro-denominated funds for the yen intervention.

Earlier this month, Bessent stated in an interview that he had assured European officials this was "merely a reallocation of our reserve assets."

However, the Financial Times reported that the ECB was only informed of the action after it had taken place.