Treasury Secretary Janet Yellen is warning lawmakers that the federal government will not be able to honor its financial obligations after Dec. 15 unless Congress votes to raise or suspend the debt limit.

In a letter to House Speaker Nancy Pelosi on Tuesday, Yellen revised her initial Dec. 3 projection. 

“To ensure the full faith and credit of the United States, it is critical that Congress raise or suspend the debt limit as soon as possible,” Yellen wrote.

The debt limit is the amount of money the U.S. government is authorized to borrow to pay its legal obligations.

Yellen has previously warned that if the the federal government cannot pay its bills, defaulting for the first time ever, it likely would trigger a “historic financial crisis,” which would include interest rates spiking, stock prices plunging, the country entering a recession and millions of jobs being lost. It could also mean seniors not collecting Social Security checks, troops going unpaid and families not receiving child tax credit payments.

In her letter, Yellen explained that the new infrastructure law signed Monday by President Joe Biden allocates $118 billion that must be transferred into the Highway Trust Fund by Dec. 15. Those funds are then invested in nonmarketable treasury securities that are subject to the debt limit.

“While I have a high degree of confidence that Treasury will be able to finance the U.S. government through December 15 and complete the Highway Trust Fund investment, there are scenarios in which Treasury would be left with insufficient remaining resources to continue to finance the operations of the U.S. government beyond this date,” Yellen wrote.

In October, Congress passed a short-term debt limit increase of $480 billion. Republicans, protesting what they view as reckless spending by Democrats, initially vowed not to support any increase or suspension of the debt ceiling, although raising the borrowing cap alone would not authorize any new spending, only pay off existing commitments made during both Democratic and Republican administrations.

Republicans wanted Democrats to address the debt ceiling in their now-$1.75 trillion spending plan, which lawmakers are trying to pass using the budget reconciliation process that requires only support from a simple majority. But Republicans finally agreed to the stopgap measure as Democrats’ negotiations over the larger bill dragged on and the default deadline approached. 

Congress has routinely raised or suspended the debt limit regardless of which party’s president is in the White House. Democrats have noted they voted three times with Republicans to do so under former President Donald Trump. 

Yellen told the House Financial Services Committee hearing last month that she supports eliminating the debt limit because she believes it’s “destructive” and poses unnecessary risks to the economy.