Five United States taxpayers and UBS clients have lodged appeals with the Swiss Federal Administrative Court in recent days, the court announced.
An avalanche of new appeals is expected in the coming weeks, as 500 cases regarding requests for judicial assistance from the US authorities were processed by the Swiss tax office by the end of November and those informed of the decision have 30 days to appeal.
The 30-day limit has been interrupted by the Christmas legal break and will resume on January 2.
In all 4,450 suspected tax fraud cases were examined by the Swiss tax authorities. Not all the decisions to share information with the US will be challenged, but the administrative court has drafted in extra staff to prepare for a significant number of contested cases, a court spokesman said.
It will take some months for the court to consider the appeals and the first decisions are not expected before July, he added.
Where appeals have not been lodged, the Swiss tax authorities will be in a position to forward the files to their US counterparts from January.
An agreement reached between Bern and Washington in August targeted, amongst others, UBS clients domiciled in the US who held non-declared accounts between 2001 and 2008.