WASHINGTON (Reuters) - House Democrats on Wednesday blasted the Trump administration for not consulting sufficiently with Congress while negotiating a mini trade deal with Japan, failing to provide details about it and refusing to testify at a congressional hearing.

FILE PHOTO: The U.S. and Japan flags fly together outside the White House in Washington April 27, 2015. REUTERS/Kevin Lamarque

Earl Blumenauer, the Oregon Democrat who heads the trade subcommittee of the House Ways and Means Committee, said lawmakers were seeking to work together with the U.S. Trade Representative’s office, but that was proving “very, very hard”.

Wednesday’s hearing on the U.S.-Japan deal signed by President Donald Trump and Japanese Prime Minister Shinzo Abe on Sept. 25 underscored growing frustration among U.S. lawmakers about what they see as moves by the Trump administration to circumvent Congress’s constitutional authority for trade policy.

Trump, a Republican, has been at odds with the Democrat-controlled House of Representatives and even some Republicans over a range of trade matters, including hefty tariffs he has slapped on China and U.S. allies, and the stalled approval of a new trade accord with Mexico and Canada.

Trade experts told the hearing that the U.S.-Japan trade deal could expose the United States to a challenge before the World Trade Organization, whose rules ban such deals unless they cover “substantially” all trade between the parties.

The Trump administration says it will keep talking with Japan about a more comprehensive deal, but Blumenauer said that might not actually happen given the 2020 presidential election and Japan’s pursuit of closer trade ties with other countries.

“This might be the high water mark with Japan,” he told reporters following testimony about many items not covered by the deal, such as autos from Japan, U.S. industrial goods and farm products such as rice, butter and sugar. “I’m afraid that ... the Japanese will move on and we’ll be left behind.”

Republicans agreed more work was needed, but said the mini deal would help U.S. farmers and ranchers, who have been hard hit by retaliatory tariffs imposed by China and other countries.

Japan’s lower house of parliament approved the trade deal on Tuesday, with its upper house likely to follow suit.

The Trump administration says the deal does not require U.S. congressional approval since Congress in 2015 granted the executive branch the unilateral right to adjust tariffs.

But Representative Bill Pascrell, a New Jersey Democrat, demanded the administration provide more details to allow Congress to exercise its required oversight.