Updated

Republicans in Congress are considering delaying a decision on President Trump’s request for $1.5 billion this year to begin construction on a border wall along the U.S.-Mexico border.

Reuters reported Tuesday that some Republicans say that the money needed for the project would likely not be in a spending bill that must pass next month to avoid a government shutdown. Sen. Roy Blunt, R-Mo., told Reuters that funding could be considered “at a later time.”

Trump promised that Mexico would pay for his wall, a demand Mexico has repeatedly rejected.

Trump's first budget proposal to Congress, a preliminary draft that was light on details, asked lawmakers for a $2.6 billion down payment for the wall. An internal report prepared for Homeland Security Secretary John Kelly estimated that a wall along the entire border would cost about $21 billion.

Congressional Republicans have estimated a more moderate price tag of $12 billion to $15 billion. Trump himself has suggested a cost of about $12 billion. Reuters reported that the wall would likely cost as much as $21.6 billion.

Lawmakers have been balking at his plans to sharply cut other federal spending to pay for the wall and other boosts to border security, while increasing military spending.

White House spokesman Sean Spicer told reporters this past week that the administration was still looking at how the wall would be funded, adding that it hasn't given up on Mexico footing the bill.