WASHINGTON — A last-minute struggle over unemployment funds is upending the painstakingly negotiated $2 trillion coronavirus stimulus bill.

The standoff means the bill faces either additional negotiations, or an amendment vote and possible procedural delays that could stall passage.

The fight pits Vermont Sen. Bernie Sanders, a Democratic presidential candidate, against a group of Republicans who want to change a brokered deal to limit unemployment pay.

Under the current deal, workers furloughed by the crisis would receive an extra $600 per week. Senate Minority Leader Chuck Schumer (D-NY) said that measure ensures workers get about 100 percent of their pay for four months if they’re laid off.

But the group of Republican senators said late Wednesday that people actually could make more than 100 percent of their pay under the provision and called for the bill to be amended to cap unemployment at 100-percent of their prior income.

The deal as written would offer a “strong incentive for employees to be laid off instead of going to work,” Sens. Lindsey Graham (R-SC), Ben Sasse (R-Neb) and Tim Scott (R-SC) said in a joint statement.

“If the federal government accidentally incentivizes layoffs, we risk life-threatening shortages in sectors where doctors, nurses, and pharmacists are trying to care for the sick, and where growers and grocers, truckers and cooks are trying to get food to families’ tables,” the GOP senators said.

The senators were later joined at a press conference by Sen. Rick Scott (R-Fla.).

Graham previously was a thorn in the side of Republican leaders negotiating the package. He opposed a White House plan to send direct checks to most Americans, pushing for a boost in unemployment pay instead. Ultimately, the deal called for $1,200 to all adults who earn up to $75,000, with smaller amounts for earners under $99,000.

The late objection threatened to wreck plans for a floor vote Wednesday when Sanders, a socialist seeking the Democratic presidential nomination, said he would delay the bill using a “hold” if the Republicans managed to water down the unemployment boost.

“In my view, it would be an outrage to prevent working-class Americans to receive the emergency unemployment assistance included in this legislation,” Sanders said.

“Unless these Republican Senators drop their objections,” Sanders continued, “I am prepared to put a hold on this bill until stronger conditions are imposed on the $500 billion corporate welfare fund to make sure that any corporation receiving financial assistance under this legislation does not lay off workers, cut wages or benefits, ship jobs overseas, or pay workers poverty wages.”

The $500 billion fund would be overseen by an inspector general and barred from issuing loans to businesses controlled by President Trump or other officials under changes already adopted at the request of Senate Democrats. Other rules prohibit boosting executive pay and stock buybacks.

The debate plunged the largest US emergency funding bill into a fresh round of chaos and dashed anticipation of speedy passage through Congress.

A deal finally seemed to be reached overnight after White House negotiators agreed to various demands pressed by Senate Minority Leader Chuck Schumer (D-NY), who won funds for hospitals and state and local governments, among other items.

It’s the latest twist in a long-running saga, with Capitol Hill aides and senators declaring since Friday that a final package was “close.”

A deal previously appeared clinched Monday, but Republicans said Democrats backed away from an initial compromise when House Speaker Nancy Pelosi (D-Calif.) unveiled a 1,400-page rival package including an extraneous list of policies ranging from environmental reforms to same-day voter registration.

Pelosi later tabled the requests and on Tuesday said she would like the House to pass by unanimous consent the massive stimulus bill to avoid calling all representatives back to Washington for a roll call vote. That plan, too, seemed unlikely when House Minority Leader Kevin McCarthy (R-Calif.) said Wednesday he agreed with senators objecting to the unemployment language.

In the US, more than 60,000 people are infected with the coronavirus, with New York suffering the worst outbreak by far. Nearly 900 US residents have died.