• Millions of Americans lost their unemployment benefits on Sunday as President Donald Trump refused to sign a $900 billion Covid-19 relief and government funding bill passed by both chambers of Congress.
• Trump's resistance to signing the bill leaves millions of Americans without unemployment coverage from two federal jobless programs and threatens a government shutdown when funding runs out on Tuesday at 12:01 a.m.
• Andrew Stettner, a senior fellow at the Century Foundation think tank, estimated up to 14 million people would collectively lose aid from the various programs that expired.

Millions of Americans lost their unemployment benefits on Sunday as President Donald Trump refused to sign a $900 billion Covid-19 relief and government funding bill passed by both chambers of Congress.

The unsigned bill provides aid for businesses and individuals struggling amid the pandemic and earmarks money for vaccine distribution and education. The bill would activate a $300 weekly boost to unemployment benefits similar to a $600 benefit outlined in the CARES Act passed in March.

The latest package is the second major effort by Congress to help Americans struggling during a recession.

Trump's resistance to signing the bill leaves millions of Americans without unemployment coverage from two federal jobless programs and threatens a government shutdown when funding runs out on Tuesday at 12:01 a.m.

Roughly 9.5 million people were dependent on the Pandemic Unemployment Assistance program that expired overnight, according to calculations by the Brookings Institution.

Andrew Stettner, a senior fellow at the Century Foundation think tank, estimated up to 14 million people would collectively lose aid from the various programs that expired. Millions more would exhaust other jobless benefits within weeks without additional stimulus relief.

"For those who can't get on another form of benefits the consequences will be swift and dangerous," Stettner tweeted on Saturday.

"These are real families caught up in the maelstrom of the pandemic scouring for shelters to live in, postponing the purchase of lifesaving medicines, and going further and further into debt," Stettner wrote.

Trump has criticized the relief bill's $600 direct payments to Americans, demanding $2,000 checks instead. Republican lawmakers quickly shot down a Democrat proposition for the higher amount in a Christmas Eve vote. Trump has also rejected foreign aid aspects of the spending package.

"I simply want to get our great people $2,000, rather than the measly $600 that is now in the bill," Trump tweeted on Saturday from Palm Beach, Florida, where he is spending the holidays at his resort. "Also, stop the billions of dollars in 'pork.'"

The president's continued refusal to sign the bill would lead to the expiration of eviction protections, living millions of renters vulnerable, as well as a delay in crucial subsidies for businesses.

Treasury Secretary Steven Mnuchin said on Monday that people could receive $600 checks as part of the stimulus package as early as this week.

However, Trump's apparent refusal to sign the bill as is will delay the distribution of those checks. It's unclear if Mnuchin, like other lawmakers who negotiated the legislation last week, was blindsided by the Trump's demand for higher direct payments.

A Treasury spokesperson told CNBC on Sunday that Trump and Mnuchin continue to speak regularly and were in contact throughout negotiations.

President-elect Joe Biden on Saturday condemned the president for delaying critical aid before unemployment benefits expired.

"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.

"This abdication of responsibility has devastating consequences," Biden said.

A group of bipartisan lawmakers who introduced the stimulus package called on the president on Sunday to sign the bill or otherwise quickly veto it in order to "allow those in favor to act before it is too late."

"Never before in your personal, professional, or political life have you been characterized as a man of inaction," the lawmakers wrote in a statement. "Now is not the time to sit idly by — please do the right thing and sign or veto this bill immediately."

House Speaker Nancy Pelosi has said that Democratic lawmakers will vote on Monday for a standalone bill to provide $2,000 direct payments to Americans.

House Democrats on Monday are also expected to review a stop-gap measure to keep the government running until Biden is sworn into office. Biden has promised more stimulus relief after he is inaugurated.

— CNBC's Steve Liesman contributed to this report