Millions of Americans saw their unemployment benefits expire on Saturday after outgoing US President Donald Trump refused to sign a $2.3-trillion (€1.9 trillion) coronavirus pandemic aid and spending package.

Trump stunned both Democrats and Republicans when he rejected the bipartisan $892-billion pandemic aid package earlier this week.  The deal would have extended special unemployment benefits that expired on Saturday for 14 million people, according to the US Labor Department.

The relief package is tied with a $1.4 trillion government spending deal. Without Trump's signature, a partial government shutdown will begin on Tuesday unless US Congress can agree to a stop-gap funding bill.

President-elect Joe Biden called on Trump to sign the bill immediately. "It is the day after Christmas, and millions of families don't know if they'll be able to make ends meet because of President Donald Trump's refusal to sign an economic relief bill approved by Congress with an overwhelming and bipartisan majority," Biden said in a statement.

He accused Trump of an "abdication of responsibility'' that has "devastating consequences."

"In just a few days, government funding will expire, putting vital services and paychecks for military personnel at risk," Biden warned. Following his inauguration on January 20, Biden also plans to push for another stimulus package to contain the pandemic and boost the economy.

Trump's refusal to sign the bill into law threatens to undo months of wrangling between Republicans and Democrats. The two sides agreed to the spending package last weekend, and Congress voted the deal through on Monday night.

Why hasn't Trump signed the COVID relief bill?

Trump, who will leave the White House on January 20, did not object to the terms of the deal ahead of Monday's vote. But he called the legislation a "disgrace" a day after it passed both chambers of Congress, saying it didn't do enough for everyday people.

Trump has demanded its one-time $600 stimulus checks to millions of Americans be raised to $2,000 — an idea that some Democrats have supported, but one that was swiftly rejected by House Republicans during a rare Christmas Eve session. He has also complained that the bill gives too much money to special interests, cultural projects and foreign aid.

Trump tweeted on Friday that he spoke with many US politicians from his Mar-a-Lago resort on Christmas Day, saying that they should "give our people the money."

What happens if he doesn't sign the spending bill?

Despite his complaints, Trump has yet to veto the bill and could still sign it before Monday.

Congress could potentially override the president's veto, salvaging months of negotiations and putting the coronavirus relief in place. Even if Trump doesn't formally veto the package, he could allow it to expire with a "pocket veto" at the end of the congressional session, leaving the next Congress to reintroduce the vote on its legislative agenda.

Democratic House Speaker Nancy Pelosi has said she would hold a roll-call vote on Monday on direct payment legislation to satisfy Trump's demand, applying pressure on Republicans who opposed the higher stimulus checks.

Trump's decision to leave the bill unsigned has not only halted the extra unemployment benefits. The coronavirus relief bill would also provide funding for US states to distribute vaccines, replenish a loan program for small businesses and provide relief funds for airlines.

This story has been updated to reflect the latest developments.

dv, sri/mm (AP, Reuters)