Ratings agency Standard & Poors said it has downgraded 15 European banks, including Bank of Ireland, Barclays, Credit Suisse and Deutsche Bank.
The move comes after European lawmakers agreed on a framework that prevents governments from having to bail out troubled banks.
The European Parliament signed off this month on new laws to make it easier - and less costly for taxpayers - to wind down problem banks, after long wrangling over rules for an industry blamed for triggering the worst economic slump in a generation.
S&P said extraordinary government support for these banks would likely diminish as regulators implement the reforms, downgrading them to 'negative' from 'stable.
The banks, many of which are systemically important, also included ABN AMRO and ING Bank.
"We observe similar powers coming into force in Liechtenstein and Norway, and already in place in Switzerland, which are not EU members," the ratings agency added.
S&P also raised its ratings on Danske Bank and Argenta Spaarbank, while keeping 'negative' outlooks on 38 banks and 'stable' outlooks on 15 banks.
It maintained its CreditWatch rating on five banks, with negative implications.