The warning came as Hispanic and liberal Democrats pressed House leaders to add provisions to the legislation strengthening protections for migrant children, changes that might render the measure even less palatable to President Donald Trump.
Many children detained entering the U.S. from Mexico have been held under harsh conditions. Lawmakers leaving a late-night meeting with Speaker Nancy Pelosi, D-Calif., said changes in the bill were possible but said leaders still hoped the House would approve the measure as soon as Tuesday.
Even so, the veto threat raised fresh questions about the bill's fate. The Senate planned to vote this week on similar legislation that has bipartisan backing, but many House Democrats say the Senate version's provisions aimed at helping migrant children are not strong enough.
"Right now, the goal is really to stop — one death is just too much," said Rep. Adriano Espaillat, D-N.Y. Last week, Customs and Border Protection Chief Operating Officer John Sanders told The Associated Press that children have died after being in the agency's care. He said Border Patrol stations are holding 15,000 people — more than triple their maximum capacity of 4,000.
Congress plans to leave Washington in a few days for a weeklong July 4 recess. While lawmakers don't want to depart without acting on the legislation for fear of being accused of not responding to humanitarian problems at the border, it has seemed unlikely that Congress would have time to send a final, House-Senate compromise to Trump by week's end.
In a letter to lawmakers threatening a veto, White House officials objected that the House package lacked money for beds the federal Immigration and Customs Enforcement agency needs to let it detain more migrants. It also complained that the bill had no money to toughen border security, including for building Trump's proposed border wall.
"Because this bill does not provide adequate funding to meet the current crisis, and because it contains partisan provisions designed to hamstring the Administration's border enforcement efforts, the Administration opposes its passage," the letter said.
Several Democrats leaving the evening meeting with Pelosi said changes in the spending bill were possible and that other provisions could end up in separate legislation. Several said changes might include language aimed at ensuring that detained children are treated humanely.
"We've got lives at stake," said Rep. Tony Cardenas, D-Calif. He said the U.S. has been "the gold standard" for treating refugees fleeing dangerous countries, "and I don't think we should compromise that at all."
Cardenas said the meeting was "intense, but no screaming, no yelling." At the meeting, Pelosi said she would review proposals to enhance protections for children, said a senior Democratic aide who spoke on condition of anonymity to describe the closed-door meeting. The aide said leaders still want the House to approve the measure on Tuesday.
Much of the legislation's money would help care for the migrants at a time when federal officials say their agencies have been overwhelmed by the influx of migrants and are running out of funds. The back-and-forth on the spending measure came as Congress' top Democrats criticized Trump for threatening coast-to-coast deportations of migrants. The remarks underscored the gap between the two sides over immigration.
Over the weekend, Trump tweeted that he would give Congress two weeks to solve "the Asylum and Loopholes problems" along the border with Mexico. "If not, Deportations start!" he tweeted. The president had earlier warned that there would soon be a nationwide sweep aimed at "millions" of people living illegally in the U.S., including families. The sweeps were supposed to begin Sunday, but Trump said he postponed them.
Pelosi, D-Calif., said the threatened raids were "appalling" when she was asked about them at an immigration event Monday in Queens, New York. "It is outside the circle of civilized human behavior, just kicking down doors, splitting up families and the rest of that in addition to the injustices that are happening at the border," she said.
On the Senate floor, Minority Leader Chuck Schumer, D-N.Y., described Trump's "chilling, nasty, obnoxious threats" and said the president "seems far more comfortable terrorizing immigrant families" than addressing immigration problems.
"I mean, my God, to threaten separating children from their parents as a bargaining chip? That's the very definition of callousness," Schumer said. It is not clear exactly what Trump, who has started his 2020 re-election bid, means regarding asylum and loophole changes. He's long been trying to restrict the numbers of people being allowed to enter the U.S. after claiming asylum and impose other restrictions, a path he's followed since he began his quest for president years ago. His threatened deportations came as authorities have been overwhelmed by a huge increase of migrants crossing the border into the U.S. in recent months.
For years, Democrats and Republicans have unable to find middle ground on immigration that can pass Congress. It seems unlikely they will suddenly find a solution within two weeks.
Associated Press writer Colleen Long and Congressional Correspondent Lisa Mascaro contributed to this report.