The European Commission's 18-month long antitrust probe into yen and euro interbank rates has been broadened to include Swiss franc-denominated swaps, posing a significant regulatory threat to financial institutions under scrutiny, the Financial Times reported on Thursday.

The commission can impose a maximum penalty of 10 percent of a company's total revenue for each rate fixing case it is involved in, the Financial Times reported on its website.

So a bank implicated in all three rate fixing cases could face fines of up to 30 percent of total revenue, the financial daily said.

On Friday, the European Union's competition commissioner Joaquin Almunia will stress his determination to pursue the cases in a speech intended to serve as a warning to financial institutions holding out against antitrust authorities, the Financial Times reported.

The paper, citing people involved in the probe, said the EU is informally exploring the potential for settlements but some companies are reluctant to open discussions over what they see as unfounded allegations.