Donald Trump is canceling nearly $1bn in spending approved by Congress, the White House announced on Friday, using a rare and contested power to axe funding for immigrant services and diversity-focused initiatives.

Trump’s office of management and budget described the funding cut as focused on “the most harmful government spending”.

Most of the cuts are focused on services for immigrants, including non-profits that serve refugees and unaccompanied minors accused of being in the country illegally. The administration says the funds are no longer necessary because illegal border crossings have diminished considerably.

A White House press release announcing the funding rescissions notes that some of the organizations are led by people who worked in the administration of Democratic president Barack Obama.

Trump’s move was condemned by senator Susan Collins, a Republican in a tough re-election campaign and chair of the Senate appropriations committee.

Collins said in a statement the action came without warning or consultation. She also said she would work to address with colleagues “these illegal actions”.

“Not only is the delay itself an impoundment that was not reported to Congress, but also it is a usurpation of Congress’s appropriations powers,” Collins said. “OMB is an agency of the executive branch. It does not get to decide which programs are worth funding.”

“This is theft from the American people, plain and simple,” Patty Murray, the Washington Democratic senator, who is vice-chair of the appropriations committee said in a statement. “These are funds Congress has delivered on a bipartisan basis and should be helping people – not cut off by a president more focused on building a ballroom than investing in families. Every Republican who voted for these bills should be furious, because [Russell] Vought is saying their votes don’t count.”

Typically, Congress can review the president’s proposed spending cuts before they take effect. But Trump made that all but impossible by announcing them with just five days left in the federal fiscal year. The government accountability office has called the maneuver, known as a “pocket rescission,” illegal.

Collins called it the latest attempt by OMB to “undermine Congress’s constitutional power of the purse”.

A year ago, Trump issued a pocket rescission for the first time in 50 years by blocking $4.9bn in congressionally approved foreign aid. The US supreme court declined to block those rescissions, saying that Trump’s authority over foreign affairs weighed heavily in its decision. This year, Trump is targeting domestic spending.

The use of a pocket rescission fits part of a broader pattern by the Trump administration to exact greater control over the US government, eroding the power of Congress.

The administration has also fired federal workers, imposed a historic increase in tariffs, and started the war in Iran without going through Congress, putting the burden on the judicial branch to determine the limits of presidential power.