The top Democratic Party leader in the U.S. House of Representatives said it is "out of the question" to give the White House so-called "fast-track" authority to negotiate massive free trade deals.
The comments made Wednesday by House Minority Leader Nancy Pelosi mean the top Democratic leaders in both houses of Congress have now expressed opposition to the trade promotion authority bill.
If the measure is not passed by Congress, it could further jeopardize the ambitious yet long-delayed Trans-Pacific Partnership free trade agreement, currently being debated by 12 countries.
The Obama administration is hoping to receive congressional approval to negotiate without having to submit every detail to lawmakers for approval. It has said this would allow countries to put their best offer on the table.
Republicans are generally more supportive of free trade agreements, arguing that bringing down global trade barriers will help open untapped markets and grow the economy.
President Barack Obama's Democratic Party is more hesitant about the multinational deals, claiming that they often favor large corporations at the expense of small businesses and export U.S. jobs overseas.
Last month, Senate Minority Leader and key Obama ally Harry Reid also broke with the White House on trade policy, announcing that he was against the fast-track legislation.
The countries negotiating the TPP are the U.S., Vietnam, Singapore, Peru, New Zealand, Mexico, Malaysia, Japan, Chile, Canada, Brunei, and Australia.
The United States-led trade pact aims to cover nearly 40 percent of global economic output when completed. The White House had hoped to finalize the deal by the end of 2013.
Another free trade deal, the Transatlantic Trade and Investment Partnership with the European Union, is also being discussed.
Many analysts believe fast-track trade authority is crucial to getting either pact passed through Congress.