Treasury Secretary Janet Yellen said the US is unlikely to reach mid-June and still be able to pay its bills, underscoring the urgency of the White House reaching a deal with Republicans to raise the debt limit.

“Well, there’s always uncertainty about tax receipts and spending,” Yellen said on NBC’s “Meet the Press” on Sunday. “And so it’s hard to be absolutely certain about this, but my assessment is that the odds of reaching June 15th while being able to pay all of our bills is quite low.”

Yellen has previously said the US could lose its ability to pay all its bills by June 1, placing the country at risk of a catastrophic default. While tax payments are expected in mid-June, getting to that date is the problem, she told NBC.

“On June 15, there are tax payments that are made that are substantial,” she said. “But early June, I interpret as before that, and it would be very difficult to get to that date.”