Yellen, in a letter to House and Senate leaders, noted that the nation’s debt ceiling — the total amount of money the federal government is authorized to borrow to pay for obligations such as Social Security and Medicare benefits — was suspended in June 2023 but will once again be in effect on Jan. 1.

The notification to Congress is the clearest sign yet that the fight to avoid default will likely take place in the early months of the new Trump administration.

Treasury Secretary Janet Yellen warned congressional leaders Friday that "extraordinary measures" will soon be required to prevent breaching the debt ceiling.