WASHINGTON (Reuters) -President Donald Trump has moved to unilaterally cancel $4.9 billion in federal funding authorized by Congress, escalating the fight over who controls the nation's spending. 

In a letter posted online late Thursday, Trump told House of Representatives Speaker Mike Johnson that he plans to withhold funding for 15 international programs, including some overseen by the State Department, the Agency for International Development (USAID).

The U.S. Constitution grants funding power to Congress, which every year has to pass legislation to fund government operations. 

The White House must secure Congress' approval if it does not want to spend that money. Congress did this in July when it canceled $9 billion in foreign aid and public media funding. 

Trump budget director Russell Vought has argued that Trump does not need Congress' approval and can withhold funds for 45 days, which would run out the clock until the funding expires at the end of the fiscal year on Sept. 30. Project Democracy, a nonpartisan advocacy group, says the tactic has not been used since 1983.

Democrats say the administration had frozen more than $425 billion in funding, which some Republicans say is illegal.

"The power of the purse rests with us and we have to take that seriously," Senator Lisa Murkowski, an Alaska Republican, said in a July interview.

But other Republicans, like Johnson, have said they support spending cuts in any form.

It is unclear if more Republicans will object.