“Any delay in making an interest or principal payment by Treasury even for a very short period of time would put the U.S. Treasury and overall financial markets in uncharted territory, and could trigger another catastrophic financial crisis,” Zames, chairman of the Treasury Borrowing Advisory Committee, wrote in a letter to Treasury Secretary Timothy F. Geithner.

Congress is facing a vote as early as next month on raising the debt ceiling. The Treasury projects that it will hit the cap on May 16, though it could use emergency measures to avoid default until about July 8.

The advisory committee includes representatives from firms including Goldman Sachs Group Inc., Bank of America Corp., Morgan Stanley and Soros Fund Management LLC. Zames’s letter, dated yesterday, was released by the Treasury Department today.

A crisis stemming from failing to raise the debt ceiling could increase the Treasury’s long-term funding costs and “the burden on the American taxpayer,” Zames wrote. A default by the Treasury, “or even an extended delay in raising the debt ceiling, could lead to a downgrade of the U.S. sovereign credit rating.”