Republicans want to allocate $1bn in public funds for Secret Service security upgrades linked to the plans.

A senior United States Senate official has put up a major roadblock for Republicans as they seek to use taxpayer money for security upgrades linked to President Donald Trump’s planned White House ballroom.

Senate Parliamentarian Elizabeth MacDonough ruled on Saturday that the proposed funding, as written in a spending bill, does not comply with the chamber’s budget rules, a Democratic lawmaker said.

Trump had repeatedly said the ballroom itself would be funded through $400m in private donations. But Republicans have sought to include $1bn for the Secret Service to pay for security improvements tied to the ballroom and other planned underground facilities.

Democrats have sharply criticised the proposal, describing it as an unnecessary luxury project at a time when many Americans are struggling with the rising cost of living, including higher fuel prices.

Trump, a former real estate developer, has promoted the project heavily, calling it “the finest building of its kind anywhere in the world”.

According to the office of Senator Jeff Merkley, the top Democrat on the Senate Budget Committee, MacDonough determined that the security funding could not be passed under the fast-track budget process Republicans are using to avoid needing 60 votes in the Senate.

Republicans hold a 53-47 majority in the chamber, meaning they would struggle to secure enough Democratic backing if the ruling stands.

Merkley said Democrats would continue challenging any attempt by Republicans to rewrite the legislation to satisfy Senate rules.

The disputed funding is part of a wider $72bn spending package focused largely on immigration enforcement, which Republicans hope to pass without Democratic support.

Democrats have opposed additional funding for Trump’s immigration policies unless broader reforms are included, especially after incidents in Minnesota in January in which US citizens were killed during operations involving federal immigration agents.

Republicans argued the security funding is necessary to protect the president. They pointed to an April incident in Washington, DC, in which an alleged gunman reportedly tried to enter a black-tie media event attended by Trump.

Trump said he expects the ballroom to be completed by September 2028, towards the end of his second term in office.