The populist Senator has pushed back on the Obama administration's trade plans before, arguing that a Trans-Pacific Partnership could undermine US sovereignty.
Now she wants to stop the Obama administration from renewing something called the trade promotion authority, or TPA.
TPA would allow the president to negotiate agreements that Congress cannot amend or filibuster, could allow a future Republican administration to repeal Wall Street reform.
Now she thinks the administration's plans to renew the trade authority, which
Warren made her point in a speech at The Institute for New Economic Thinking on Tuesday.
"I very much hope that a Democrat wins the White House in 2016 and again in 2020. But what happens if we have a Republican president in 2016 or 2020?" she said, according to Politico.
"We are already deep into negotiations with the European Union on a trade agreement, and big banks on both sides of the Atlantic are gearing up to use that agreement to water down financial regulations."
If international trade and Wall Street bank regulation sound completely unrelated, there is some foundation to her argument.
A coalition of American and European business groups, including the US Chamber of Commerce, are reportedly lobbying to include some amendments to bank regulation in the Transatlantic Trade and Investment Partnership with Europe.
Meanwhile, the Trans-Pacific Partnership, a 12-nation accord that includes countries on four continents, has faced pushback for unrelated reasons - mainly from unions worried about job losses.
Warren took it a step further, co-writing a letter to the president with Senator Sherrod Brown (D-OH) referring to the agreement as a "secret" deal.
Her latest argument, not against the agreement but against the trade promotion authority itself, is just the latest in her ongoing effort to protect the 2010 Dodd-Frank bank regulation - a theme she regularly hits on.
The Obama administration isn't taking Warren's criticisms well.
One official quoted by Politico called her accusations "baseless" and "desperate," with "no bearing or relation to anything we are doing."