The seven-member council today said in a statement that the agreement sets "parameters for cooperation" so that Swiss banks can cut deals to avoid US charges for shielding tax cheats.
But it said the data "can only be supplied within the scope of existing agreements with the US in the area of double-taxation via administrative assistance".
Last month, Switzerland's lower house of parliament rejected a proposal from Finance Minister Eveline Widmer-Schlumpf and the rest of the Cabinet to relax secrecy laws, despite the upper chamber's approval.