Democrats controlling the House have teed up a vote next week to block President Donald Trump from using a national emergency declaration to fund a wall along the U.S.-Mexico border, accelerating a showdown in Congress that could divide Republicans and lead to Trump's first veto.

The Democrats introduced a resolution Friday to block Trump's declaration, and House Speaker Nancy Pelosi said the House would vote on the measure Tuesday. It is sure to pass, and the GOP-run Senate may adopt it as well. Trump quickly promised a veto.

"Will I veto it? 100 percent," Trump told reporters at the White House.

Any Trump veto would likely be sustained, but the upcoming battle will test Republican support for the president's move, which even some of his allies view as a stretch — and a slap at lawmakers' control over the power of the federal purse.

Pelosi, D-Calif., said she'd honor her oath of office and uphold the Constitution, adding, "I wish he would have the same dedication to that oath of office himself." Speaking to reporters in Laredo, Texas, she said, "This is a path I would not recommend he go down. I don't expect him to sign it, but I do expect us to send it" to him.

House GOP leaders will urge rank-and-file Republicans on Monday to oppose the measure, Republican aides said. If all Democrats and at least 55 Republicans vote for it, it would pass by a veto-proof margin — a two-thirds majority. The aides spoke on condition of anonymity to describe leaders' plans.

A staff aide introduced the measure during a short pro forma House session in which Rep. Don Beyer, D-Va., presided over an almost-empty chamber.

"What the president is attempting is an unconstitutional power grab," said Rep. Joaquin Castro, D-Texas, the sponsor of the resolution, on a call with reporters. "There is no emergency at the border."

Trump's declaration of a national emergency gives him access to about $3.6 billion in funding for military construction projects to divert to border fencing. But the administration is more likely to tap funding from a federal asset forfeiture fund and Defense Department anti-drug efforts first.

Trump's edict is also being challenged in the federal courts, where a host of Democratic-led states such as California are among those that have sued to overturn Trump's order. The House may also join in.

For Democrats, the vote is another chance to challenge Trump over funding for a border wall, the issue that was central to the 35-day government shutdown. It also puts some Republicans from swing districts and states in a difficult spot, as many have expressed misgivings about Trump's action despite their support for his border security agenda.

Should the House and the Senate initially approve the measure, Congress seems unlikely to muster the two-thirds majorities in each chamber that would be needed later to override a Trump veto.

Republicans who oppose the emergency declaration on the first vote might switch and rally behind a Trump veto. But an initial roll call with strong numbers of Republicans defying him would be an embarrassing show of GOP rifts.

The measure to block Trump's edict will be closely watched in the Senate, where moderates such as Susan Collins, R-Maine, and Lamar Alexander, R-Tenn., have signaled they would back it. Senate Majority Leader Mitch McConnell, R-Ky., is only a reluctant supporter of Trump on the topic.

Trump's GOP allies promised they would uphold any veto denying Democrats the two-thirds votes required to overcome one.

"Democrats' angst over Congress' power of the purse is unwarranted, especially since the commander in chief's authority to redirect military funds for a national emergency is affirmed in a law passed by their own branch," said top House Judiciary Committee Republican Doug Collins of Georgia.

The battle is over an emergency declaration Trump issued to access billions of dollars beyond what Congress has authorized to start erecting border barriers. Building his proposed wall was the most visible trademark of Trump's presidential campaign.

Congress last week approved a vast spending bill providing nearly $1.4 billion to build 55 miles (89 kilometers) of border barriers in Texas' Rio Grande Valley while preventing a renewed government shutdown. Trump had demanded $5.7 billion to construct more than 200 miles (322 kilometers).

Trump wants to use an emergency declaration and other authorities to gain access to an additional $6.6 billion for wall building. That money would be transferred from a federal asset forfeiture fund, Defense Department anti-drug efforts and a military construction fund. Federal officials have yet to identify which projects would be affected.

Two senior defense officials said Friday that it will take months for the Pentagon to assess a still-to-come Department of Homeland Security proposal to siphon anti-drug funds to build barriers, sign contracts and begin construction. The officials spoke on condition of anonymity to provide information that has not yet been made public.

Castro, the resolution sponsor, said that he has already garnered support from most of the House and has at least one GOP sponsor, Rep. Justin Amash of Michigan.

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Associated Press writers Nomaan Merchant in Houston and Lolita C. Baldor and Alan Fram in Washington contributed to this report.