Just as markets were digesting the $2.6 billion penalty imposed on Credit Suisse for helping American clients avoid taxes, news from Brussels suggests that yet another big fine is looming for a few other banking giants. Today the European Commission accused JPMorgan, HSBC, and Crédit Agricole with rigging euro interest rates, alleging that they acted in a cartel to manipulate Euribor, a key interbank lending rate.

The three banks refused to settle the antitrust case in December last year, when the commission fined eight other banks and brokers a record €1.7 billion ($2.3 billion) for their roles in the rate-rigging cartel. Settling the case saved the accused 10% of the headline fine, on top of other discounts based on their degree of co-operation with regulators.

JPMorgan, HSBC, and Crédit Agricole must now answer the commission’s charges without the offer of leniency that comes from settling. That said, throughout the financial crisis European regulators have been seen as softer than their American counterparts, with Brussels wielding more limited powers and showing less of an appetite to impose big penalties. Even after settling with the EU in last year’s euro interest rate case, Société Générale is challenging its €446 million fine in court, alleging “a manifest error of assessment” in calculating it.

The three banks that were charged today will hope to benefit from the eurocrats’ presumed timidity. In theory, EU cartel fines carry a penalty of up to 10% of a company’s global revenue, which would imply a combined fine of more than $18 billion, according to the bank’s latest annual results.

But the commission is highly unlikely to ask for this much in damages, and the depressing regularity with which big banks land in legal trouble these days means that they are well prepared to pay the penalties. From interest rate-rigging to mortgage mis-selling, tax avoidance, foreign-exchange manipulation, money laundering and much else besides, banks now operate under the constant threat of large fines, and they’ve built up enormous litigation reserves to cope.

The three banks charged by the EU today all saw their shares wobble slightly, but they had fallen by less than 1% at the time of writing. Shares of Credit Suisse actually gained around 1% following the news of its multi-billion-dollar fine.