Top Democratic senators told President Barack Obama that he must be ready to take "any lawful steps" to ensure that the United States does not default on its debt payments -- even if it means acting without approval by Congress.
The White House has said it believes it does not have constitutional authority to raise the debt ceiling unilaterally.
In an excerpt of the letter to Obama that was made available on Friday, the Democratic senators wrote: "We believe you must be willing to take any lawful steps to ensure that America does not break its promises and trigger a global economic crisis -- without congressional approval, if necessary."
At issue is whether the Constitution permits the president to ignore the $16.4 trillion cap on government debt under the 14th Amendment. It states, in part, that the "validity of the public debt of the United States ... shall not be questioned."
The White House has said emphatically that it does not believe that the 14th Amendment permits Obama to ignore the debt cap on U.S. borrowing. The government reached that cap last month and is juggling the books to buy additional time for Congress to act.
One Senate Democratic aide said other legal options are being explored. The Treasury is shuffling funds around to continue paying government bills. But those accounting maneuvers are due to run their course around mid-February.
Republicans have said they will only raise the debt ceiling if it is accompanied by massive spending cuts and changes to big government programs Social Security and Medicare.
"We believe that you must make clear that you will never allow our nation's economy and reputation to be held hostage," said the letter signed by Senate Majority Leader Harry Reid and the three other Democratic leaders in the Senate.