NEW YORK ( TheStreet) -- Ratings agency Standard & Poor's cut its rating of Goldman Sachs ( GS), Bank of America's ( BAC) Merrill Lynch unit and Citigroup ( C) long term debt from A to A-, and put their ratings on a "negative" watch, according to a statement issued after the market close Tuesday.

The new ratings were part of a sweeping change to its rating methodology for 37 financial institutions published on Nov. 9 . The changes also led to a Wells Fargo ( WFC) downgrade from AA- to A+ and a JPMorgan ( JPM) cut to A from A+, among a host of bank cuts spanning the world.

They include Rabobank of the Netherlands, which lost its vaunted AAA rating and mega-banks from Switzerland's UBS ( UBS), to Spain's BBVA ( BBVA) and Barclays ( BCS) of Britain among others.

For Goldman, Bank of America and Citigroup, the cut may prove to be costly. According to Bloomberg reports, Bank of America said in a November filing with regulators that if its rating were cut a notch, it would have to post $5.1 billion of additional collateral and other payments on its trades.

While Bank of America Merrill Lynch holds the same A- rating with S&P as competitors Goldman and Citigroup, Moody's holds its rating at Baa1 - below the A3 and A1 levels it ascribes to Citigroup and Goldman respectively.

Bank of America shares fell over 1% in afterhours trading after the company hit its 2011 low of $5.03 in Tuesday trading.

In its revised calculations, S&P raised its outlook on the ratings of Credit Suisse ( CS), Deutsche Bank ( DB) and State Street ( STT) from "negative" to "stable."

-- Written by Antoine Gara in New York