Janet Yellen, the US Treasury Secretary, said on Sunday that June 1 remains a "hard deadline" for raising the federal debt limit, however, the chances that the government will collect enough revenue to make it to June 15, when additional tax revenues should come in, are rather low.

Yellen told NBC that Americans will have to make tough payment choices if Congress fails to raise the $31.4 trillion debt ceiling before the Treasury runs out of cash.

"I indicated in my last letter to Congress that we expect to be unable to pay all of our bills in early June and possibly as soon as June 1. And I will continue to update Congress, but I certainly haven't changed my assessment. So I think that that's a hard deadline," she said.