A $600 (£459) jobless benefit paid weekly to tens of millions of unemployed Americans expired overnight after Republicans and Democrats failed to reach a deal on its extension.
Friday was the deadline for an agreement on the coronavirus relief, which tops up state benefits that are mostly far below $600.
Republicans want a smaller relief plan than one passed by the Democrat-controlled House of Representatives.
Talks will continue on Saturday.
Unemployment has soared during the coronavirus pandemic, with 30 million Americans currently collecting jobless benefits.
The US economy shrank at a 32.9% annual rate between April and June – the sharpest decline for decades.