WASHINGTON—The government’s just-approved budget deal takes $1.5 billion from a fund for crime victims and uses it instead to help pay for federal spending, drawing on a growing reserve collected from settlements with banks and major corporations.

The unprecedented transfer, part of closed-door negotiations between the Obama administration and congressional leaders, has raised the ire of advocates. They say it violates the integrity of a decades-old program that funds safe havens for domestic violence victims, counseling for abused children and financial aid for murder victims’ families, among other programs.

The administration and Republican congressional leaders averted a partial government shutdown by striking a two-year budget deal approved by Congress last week. As part of the pact the Crime Victims Fund will lose $1.5 billion to the general treasury, Obama administration officials said.

Since the fund’s creation in 1984 by the Victims of Crime Act, it has gathered money from fines imposed on criminals and set it aside to pay for services for crime victims.

But during the Obama administration, as major banks and corporations paid large sums to settle Justice Department investigations, the fund ballooned from about $3 billion to nearly $12 billion at the end of the 2014 budget year, according to the department.

The fund’s growing size has presented policy makers with a dilemma. When the fund began, the government paid out almost every dollar it received. But in 2000, Congress began capping the amount paid each year to ensure a steady stream of money for victims’ services.

From 2000 to 2008, the fund grew from $1 billion to $3 billion. As its balance kept rising, White House accountants were able to use the cash in an accounting move to offset government spending. Now, Congress and the White House have struck a deal to go further, by agreeing to withdraw some 10% of the money to directly fund the government.

Victims’ advocates say the move could set a dangerous precedent and encourage lawmakers to keep dipping into a pot of money intended to help crime victims, not to pay government bills.

Two years ago, the fund distributed about $745 million for victims services. That jumped last year to almost $2.4 billion, most in grants to state and local groups that provide counseling, aid or other services.

The proposed White House budget for fiscal 2016, which started Oct. 1, would give $1 billion to victim-services groups. Budget officials said it was a coincidence that the proposed reduction from last year’s $2.4 billion is about the same as the amount to be transferred out of the fund to general spending.