"There could be some impact of a couple of days," Mnuchin said in a CNBC interview.

The U.S. Treasury technically hit the debt ceiling in March and has been using loopholes it calls “extraordinary measures” to continue borrowing in order to pay its bills since then. The Treasury had said those measures would be exhausted on Sept. 29 , which would lead to a U.S. debt default without Congressional action.

The date is calculated based on how much revenue the government brings in, how much it spends and how much it has to borrow to make up the difference.

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If Congress passes a previously unplanned multi-billion-dollar spending measure to help victims of Harvey, however, it may reach that limit sooner.

Those few days could add significant pressure to Congress, which only has 12 legislative days planned in the month of September, and faces several crucial deadlines.

The fiscal year ends on Sept. 30 , and without new spending provisions, the government will shut down afterward. Congressional leaders have increasingly been leaning toward passing a three-month stopgap measure to continue current spending levels for the first three months of the new fiscal year, and raising the debt ceiling in the same bill.

If the debt deadline moves up just four days, for example, it could significantly narrow the window Congress has to pass the legislation when it returns from its August recess on Sept. 5 .