Its decision to downgrade the lenders was due to their “direct reliance on the US government” S&P said, according to the BBC.
It follows the agency’s move to strip the USA of its top AAA rating for the first time ever on 5 August.
David Beers, head of sovereign ratings at S&P, said: “We still think that the risks to the rating are still pitched to the downside – that’s why we have a negative outlook. We don’t anticipate a scenario at the moment in which the US would quickly return to AAA.”
However, US Treasury Secretary Timothy Geithner has criticised the decision, telling NBC that S&P had shown “terrible judgement” and “a stunning lack of knowledge about basic US fiscal math”.