(Bloomberg) -- The leaders of the committee of bond dealers and investors that regularly advises the U.S. Treasury Department stressed to Secretary Janet Yellen on Tuesday their concern over potentially dire risks to the financial system if Congress fails to lift or re-suspend the debt limit.

The U.S. debt cap kicked in August after a prior two-year suspension ended, forcing the Treasury to tap extraordinary measures to avert breaching its borrowing capacity. Treasury Secretary Yellen has said that government will otherwise run out of money to pay its bills sometime in October if Congress doesn’t act. 

“If left unresolved, this situation would put the U.S. government at risk of missing debt payments -- an outcome that would have severe consequences for the U.S. Treasury market and, ultimately, for the U.S. economy,” Beth Hammack, chair and Brian Sack, vice chair of the Treasury Borrowing Advisory Committee wrote in the letter posted on the Treasury’s website. “Even if default were avoided, continued negotiations over the debt limit could cause needless volatility, create additional operational expenses for market participants, and do lasting damage to the Treasury market.”

House Democrats are trying to push through a bill that would suspend the U.S. debt ceiling until after the 2022 congressional elections and temporarily fund the government to avert a shutdown after the end of this month.

A protracted battle over the debt limit could also cast doubts of the U.S.’s creditworthiness, Hammack and Sack wrote. It could become difficult to even buy or sell some Treasuries, given uncertainty over payment status, they warned.

S&P Global Ratings in 2011 downgraded the U.S. after a protracted -- but ultimately successful -- battle to lift the debt limit.

“We encourage you to continue working with Congress to raise, suspend, or eliminate the debt ceiling immediately,” Hammack and Sack wrote. “To default would be unthinkable, but even to risk that outcome would be reckless and irresponsible.”

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