The 23 legislators sent a letter to President George W. Bush saying the so-called "123" operating agreement, which reportedly allows India to reprocess spent nuclear fuel, could end up violating US law.

"The agreement for nuclear cooperation is subject to the approval of Congress, and any inconsistencies between the agreement and the relevant US laws will call congressional approval deeply into doubt," said the letter from the 23 members of the House of Representatives.

Edward Markey, co-chairman of the House Bipartisan Task Force on Nonproliferation, sounded his own warning.

"If the 123 agreement has been intentionally negotiated to side-step or bypass the law and the will of Congress, final approval for this deal will be jeopardized," Markey said.

Details of the agreement have been kept under wraps since it was finalized in Washington last week by senior officials of the two countries.

The nuclear deal was agreed upon by Bush and Indian Prime Minister Manmohan Singh two years ago to highlight strategic ties between the world's two biggest democracies.

The Congress approved the deal in principle last year and a bill to that effect was signed into law by Bush, but there was a delay in finalizing the operating agreement, which has to be approved again by Congress.

India has stood fast against accepting any curbs on its reprocessing of spent nuclear fuel.