The bonds' underlying rating was dropped from Baa3, an investment grade, to Ba1, a speculative grade, by Moody's last Thursday.
Standard and Poors cut the bonds from BBB to BB+ on Tuesday while still giving them a "stable outlook."
The Mets sold $613.1 million of three types of bonds in 2006 and an additional $82.28 million of bonds last year. Ambac Assurance Corp., the company having financial difficulty, insured $547.6 million of the 2006 PILOT bonds (payment in lieu of taxes).
"We lowered all the bonds ratings because the 2006 PILOT bonds do not have a reserve fund with adequate liquidity to support any disruption in project cash flow," Standard & Poors said. "Because Ambac is currently rated speculative grade, the creditworthiness of the debt service reserve fund supported by the surety policy is below the creditworthiness of the bonds."
S&P said the stable outlook "reflects the expectation that the project will perform in line with expectations."
The $800 million ballpark opened last year, and the Mets went a dismal 72-90.
"This is related specifically to Ambac, which insures the 2006 bonds, and is not based on our operations or the strength of the underlying credit," the Mets said in a statement.