US President George W Bush would veto a second congressional bill on the war in Iraq that links funding to progress there, his spokesman has said.
Mr Bush has already vetoed one funding bill for Iraq
The bill, currently being drafted by Democratic lawmakers in the House of Representatives, funds operations in Iraq until the end of July.
But it would then give Congress the option of cutting off money if the security situation did not improve.
Mr Bush has already vetoed a bill that linked funding to a troop withdrawal.
White House spokesman Tony Snow said that Mr Bush would veto the new bill in its current form.
"There are restrictions on funding and there are also some of the spending items that were mentioned in the first veto message that are still in the bill," he said.
Targets for progress
The bill would ring-fence around half of the money that Mr Bush has requested to fund the war in Iraq.
Lawmakers would then vote in July on whether to release this money on the basis of a report from Mr Bush on progress towards political, economic and security targets.
US Defence Secretary Robert Gates said that a funding cut in July would cripple the Pentagon.
"We will have forward-spent so much money to keep the troops in the field by that time that the truth is... I would have to shut down significant elements of the Department of Defence in August and September because I wouldn't have the money to pay salaries," he said.
The BBC's James Coomarasamy in Washington says that it is not just the White House that is opposed to this new two-step approach.
Some key Senate Democrats, including the head of the Armed Services Committee, Carl Levin, have expressed their concern.
Mr Levin said it was simply not practical to keep the US troops on such a short funding lease.
The bill could come to a vote in the House of Representatives as early as Thursday.