"We've been using extraordinary measures for several months now and our ability to do that is running out," Yellen told an American broadcaster, when asked whether her office still had some extraordinary steps in stock.
She noted that US President Joe Biden may invoke the 14th amendment to the US constitution that allows him to avoid default bypassing the position of the US Congress.
"We should not get to the point, where we need to consider whether the president can go on issuing debt, this would be a constitutional crisis," Yellen said.
The 14th amendment to the constitution of the United States provides that "the validity of the public debt of the United States, authorized by law, including debts incurred for payment of pensions and bounties for services in suppressing insurrection or rebellion, shall not be questioned." This section allows the country's president to resolve the debt issue without coordinating with the US Congress.
Earlier in May, the US Department of the Treasury said the US government will likely begin defaulting on its debt by June 1 if the so-called congressional limit on the country's debt servicing is not raised by then.
In late April, House Republicans passed legislation to raise the debt ceiling in exchange for cuts in federal spending and other measures to reduce the deficit. However, Senate Democrats and US President Joe Biden rejected the proposal, saying it had no chance of becoming law. Inversely, House Speaker Kevin McCarthy said that a "no-strings-attached" debt limit increase would not pass the lower chamber.
Biden is scheduled to meet with McCarthy and other congressional leaders next week to negotiate the raising of the US debt limit.