Standard & Poor’s revamped its ratings criteria and lowered the ratings of 15 U.S. and European banks by one notch on Tuesday, leaving 20 more bank ratings unchanged and raising two by a notch apiece.

The overhaul of criteria used to determine bank ratings had been in the works for more than a year, according to a Reuters report, and the company had warned markets that the move was on its way. The action could hardly come at a worse time for banks, however, in a nervous market in which bank stocks have been pummeled. Guy LeBas, chief fixed income strategist at Janney Montgomery Scott in Philadelphia, was quoted saying, “Banks could see higher funding costs.”

Among the institutions whose ratings were cut by a notch were JPMorgan Chase & Co. (JPM), Bank of America (BAC), Citigroup (C), Wells Fargo & Co. (WFC), Goldman Sachs Group (GS), Morgan Stanley (MS), Barclays (BARC), HSBC Holdings (HSBA) and UBS (UBSN). Dozens of subsidiaries of the re-rated banks also saw their ratings change.

Earlier in November, S&P had said it would be rolling out new ratings for more than 750 banks across the globe, beginning with the largest. More announcements will follow in weeks to come. The changes for this first batch were more severe than S&P had originally predicted for all banks—at first officials at the ratings agency had forecast that 20% of all banks would suffer a drop in ratings, 20% would rise and 60% would be unchanged.

The move comes as S&P tries to repair its own reputation, which suffered considerable damage after it was found to have rated securities backed by subprime mortgages as triple-A. Banks are now compelled to update their own contingency plans in case of downgrades, as well as offering broader disclosure on their exposure to ratings triggers built into obligations bound to assets among their holdings.