Moody's rating agency lowered the credit outlook for 82 European banks on Friday because a new EU law makes banks mutually responsible for risks in the event of another crisis.
The decision highlights the difficulties of cleaning up and underpinning the banking system which was a focus of public and political anger during the recent crises in the eurozone.
The new rules are intended to ring-fence banks which could trigger panic in the system, as happened during the financial crisis, and to reduce the risk of taxpayers having to bail out banks to prevent them from wrecking economies.
The agency lowered its outlook for the 82 banks to be able to hold on to their current credit ratings from "stable" to "negative".
It lowered the outlook from "positive" to "stable" for two banks, and held a "positive" outlook for four banks.
The country most affected was Germany, where 12 banks were affected by the lowered outlooks.
Among other countries affected were France with 10, Austria eight, Sweden five in Sweden, and Italy four.
Three of the banks are in the Netherlands, two in Spain, and one in Britain.
The decision by Moody's is an unwelcome development for the banks concerned since it comes against a background of so-called stress tests by the European Central Bank which has already pushed banks to hurry to strengthen their balance sheets to meet new international regulations.
The ECB is exercising a new responsibility to oversee the ability of leading banks in the eurozone to withstand pressures such as occurred during the financial and then the eurozone debt crises.
The decision also comes at a time when the ECB is concerned that the banks, while strengthening their risk profiles, are holding back on lending to businesses in the eurozone, and may well ease its monetary policy next week partly with this in mind.
Public opinion in many countries was outraged at the problems, and high salaries in the banks which are widely blamed for being a factor in the crisis, and in the budget cuts and tax rises which followed. There was widespread pressure on governments to tighten rules across the European Union banking sector.
- Outlooks could fall further -
In a number of eurozone countries, for example Ireland, Greece and Spain, but also in non-euro Britain, banking systems had to be rescued with taxpayers' money from European Union countries, and the link between banks and public finances pushed up borrowing rates on the eurozone bond market.
To break this link, which drove a vicious spiral of a fall in bond values which worsened the value of banks' balance sheets, European Authorities have agreed, and now enacted a directive.
This enacts the new arrangements to close down a bank which could spread domino-style damage, under overall arrangements which create a safety fund.
Moody's said it had lowered the outlook for the 82 banks following "the recent adoption of the Bank Recovery and Resolution Directive (BRRD) and the Single Resolution Mechanism (SRM) regulation in the EU."
The agency said that it was not yet evident that the new rules would be effective in dealing with the difficulties of rescuing big international banks which got into trouble.
It said it had taken its latest decisions given "the explicit inclusion of burden-sharing with unsecured creditors as a means of reducing the public cost of bank resolutions."
The new rules meant that "the balance of risk for banks' senior unsecured creditors has shifted to the downside."
Moody's said that it would monitor how the new system to avert a threat to the banking system shaped up in the way it worked in detail, but "the probability has risen" that the credit outlook for the banks would be revised downwards.