According to a report in the Wall Street Journal, documents were seized from the offices of many other leading banks, in "dawn raids" authorized by the European Commission.
The banks played down the significance of the raid. "It was more of a visit than a raid," said an executive at one bank in London where EU officials showed up unannounced. They asked for information and were escorted inside.
Under scrutiny is the Euro Interbank Offered Rate, or Euribor, which is a benchmark interest rate set by leading banks to determine interest rates on trillions worth of loans and debts inside the eurozone. The banks are suspected of conspiring to manipulate the rate.
The EU investigators have the power to enter buildings and seize documents when violations are suspected. It is believed that Wednesday's raids are part of an effort to better understand the mechanics of the Euribor rate and uncover foul play in the banking sector.
Cedric Quemener, manager of Euribor EBF, the group in Brussels that administers the Euribor interest rate, said he wasn't worried about the investigation because Euribor is based on information collected from so many banks.
"I'm not fearing it," Mr. Quemener said Tuesday.