Chuck Schumer, the US Senate’s top Democrat, has vowed to oppose a Republican plan to spend $1bn on security improvements for the ballroom Donald Trump is seeking to build on the White House’s former East Wing.

The money is set to be included in a measure Republicans plan to pass that would allocate about $70bn to the federal agencies leading Trump’s mass deportation campaign, with the intention of keeping them operational through the remainder of the president’s term.

“That is what today’s Republicans have become: Republicans – asking working families to pay the price while Donald Trump pockets the perks,” Schumer, the Senate minority leader, wrote in a letter to Democratic senators.

“Let me make one thing very clear: Senate Democrats will not let them jam through this bill without making them answer for their endless cost hikes, healthcare cuts, and every dollar diverted from American families to Trump’s priorities. Democrats will fight the Republicans’ reconciliation bill with every tool we have.”

Chuck Grassley, the Republican chair of the Senate judiciary committee, last week included the ballroom security money in a resolution outlining his committee’s plan for the immigration enforcement spending bill. The committee is expected to consider the resolution at a hearing on Tuesday.

The $1bn is intended for the US Secret Service to spend on security enhancements related to the “East Wing modernization project”, as the Trump administration refers to the White House ballroom. Trump has claimed that the ballroom itself, which is estimated to cost $400m, will be funded by donations from individuals and major businesses including Meta, Apple, Amazon, Lockheed Martin, Microsoft, Palantir, Google and Comcast.

But Schumer argued the money would enable the president to continue his remaking of the executive mansion, which also faces a challenge in federal court.

Republicans are advancing the legislation using the reconciliation procedure, which can circumvent a filibuster by Democrats in the Senate and pass with a simple majority. Schumer said Democrats will propose amendments to the bill and challenge its compliance with the rules of reconciliation, with the intention of forcing Republican lawmakers into taking positions that could hurt them with voters ahead of the midterm elections.

“We will force vote after vote to make the choice unmistakable: will Republicans vote to help American families – to lower costs, to restore savage health care cuts, to roll back cost-spiking tariffs – or will they vote to fund Trump’s gaudy ballroom?” Schumer wrote.

The immigration spending bill is a key plank of the Republican plan that late last month saw Congress vote to reopen the Department of Homeland Security (DHS) after a funding impasse that stretched for 75 days. Democrats had refused to approve the department’s appropriations unless the Trump administration agreed to new restrictions on immigration enforcement operations, but the two sides were unable to reach a compromise.

The Democratic minority eventually agreed to vote for an appropriations measure for DHS, so long as funding for Immigration and Customs Enforcement (ICE) and Customs and Border Protection was excluded. The Republican majority will, using the reconciliation procedure, move to approve spending by both agencies through 2029.