The government says it will take part in a United States civil case against bank UBS, which is being accused of facilitating massive tax evasion by wealthy Americans.
The Swiss will protect their "sovereign interests" according to a statement, by instructing an American law firm to draft an "amicus curiae" brief explaining Switzerland's legal position.
"Amicus curiae" is the name given to a person or organisation that participates in a court action but is not a party to the action.
An amicus curiae can provide the court with detailed information or expertise.
Switzerland's biggest bank has accepted responsibility for helping thousands of Americans hide assets from the US government but has rejected requests to divulge the names of all US citizens who maintain secret accounts with the bank.