More than half the new Democratic lawmakers in the U.S. Congress have signed a letter opposing the White House's request for authority to fast-track trade deals and an ambitious Pacific trade pact.

Nine of the 16 new Democrats in the House of Representatives wrote to President Barack Obama on Wednesday to express "serious concerns" about fast-track, which limits Congress to a yes-or-no vote on trade agreements in exchange for setting negotiating objectives.

"Our constituents sent us to Congress to get American trade policy back on track - not give away its authority to do so," said the letter.

They also said the Trans-Pacific Partnership, which the United States is negotiating with 11 other trading partners, delved deeply into non-trade matters such as land use, copyright and patent standards.

Obama called for fast-track authority in his State of the Union address on Tuesday night, saying the United Statesand not China should set the rules for trade in the Asia-Pacific region. (Reporting by Krista Hughes; Editing by Sandra Maler)