WASHINGTON (AP) — Republicans returning to Washington on Monday are facing questions about a $1 billion Senate security proposal that could help pay for President Donald Trump's ballroom as Democrats say they will try to defeat it.

Senate Republicans added the money for White House security to a spending bill that would restore funding for immigration enforcement agencies that Democrats have blocked since February. The steep security proposal was put forward after a man was charged with trying to assassinate Trump at the White House Correspondents' Association dinner last month.

READ MORE: Senate Republicans look to fund $1 billion in security upgrades for Trump's ballroom

Republicans are using a partisan budget maneuver to push the spending legislation through Congress without any Democratic votes. But in a letter to colleagues Monday morning, Senate Democratic leader Chuck Schumer said Democrats will fight it in other ways, including by pushing the Senate parliamentarian to strike the ballroom security money from the budget bill and offering amendments forcing Republicans to vote on it.

"The Republican-controlled Congress is preparing to answer this moment with a deficit-busting, party-line bill that pours billions more taxpayer dollars into a rogue ICE operation and a billion-dollar ballroom, while doing nothing to end the illegal war in Iran or ease the Republican affordability crisis bearing down on working families," Schumer wrote in the letter.

Educate your inbox

Subscribe to Here’s the Deal, our politics newsletter for analysis you won’t find anywhere else.

It's unclear if the security money will even have enough backing among Republicans. The House has not released its bill yet, but the Senate is expected to start voting on its version of the legislation this week.

While most GOP lawmakers have remained quiet on the proposal as they spent their recess out of Washington, some have publicly questioned whether they would support it.

"I'm going to look at it very carefully and make sure those things are in the national interest," said Rep. Rob Wittman, a Virginia Republican who was in the Capitol last week to briefly gavel in a pro forma session of the House.

"I want to know the exact nature of the expenditures that would go there for security. So I think it's a little premature to look at that and say, you know, yes or no to it," Wittman said.

Wittman wants to better understand the details of the Senate proposal and "how it's part of what the total construction cost is," he said.

Trump has said the ballroom's construction would cost $400 million and use private funds, but he had not proposed a number for security costs.

The Senate bill would designate the money for the U.S. Secret Service, including for "security adjustments and upgrades" related to the ballroom project, which Trump and other Republicans have been pushing since Cole Tomas Allen was charged with storming the April 25 media dinner at the Washington Hilton with guns and knives.

The legislation says the money would support enhancements to the ballroom project, "including above-ground and below-ground security features," but specifies it may not be used for non-security elements.

White House spokesperson Davis Ingle praised Republicans last week for including the money for the "long overdue" project, saying it would "provide the United States Secret Service with the resources they need to fully and completely harden the White House complex, in addition to the many other critical missions for the USSS."

The White House has said in court documents that the East Wing project would be "heavily fortified," including bomb shelters, military installations and a medical facility underneath the ballroom. Trump has said it should include bulletproof glass and be able to repel drone attacks.

The National Trust for Historic Preservation has sued to block construction of the project, but a federal appeals court said last month that it can continue in the meantime.