U.S. Senate on late Monday night rejected the latest House bill to delay part of the healthcare law and fund the government through mid-December, as the federal government teeters toward a shutdown.

By a vote of 54-46, the Democratic-controlled Senate rejected the changes to Obamacare and again sent back to the House a "clean" funding bill to keep the U.S. government operating beyond Sept. 30, when the current fiscal year expires.

With less than two hours to go before the mid-night deadline, the Congress remains in a budget stalemate, with lawmakers of the both parties squabble over who to blame.

Senate Majority Leader Harry Reid, who spearhead the Democratic strategy in the legislative battle, called the Republicans to stop sending provisions to the Senate that would undermine the healthcare law.

The House Speaker John Boehner said earlier that the GOP lawmakers were fighting to shield Americans from the "unknown consequences and unknown damage" of the Affordable Care Act, known as Obamacare.

In an unscheduled statement on Monday afternoon, Obama said a shutdown will have a "very real economic impact" on Americans. "Past shutdowns have disrupted the economy significantly. This one will too," he added.

Local media said Obama talked with the Congressional leaders over telephone on Monday night, but it is unknown whether any progress has been made.

Failure to reach an agreement on terms for funding the government by midnight Monday would force the first partial U.S. government shutdown since 1996.