WASHINGTON -- The U.S. government could exhaust its ability to pay its bills in the first half of September, according to a new estimate, creating pressure on Congress to suspend or raise the federal debt ceiling sooner than lawmakers had expected.

Weaker-than-expected revenue collections have caused the so-called X date to come sooner than previous projections, according to the Bipartisan Policy Center, a research group that released the estimate on Monday. In May, the same group had predicted the government would hit the limit in October or early November, though the Treasury Department also said in May that a late-summer deadline was possible.