At 09:45 BST shares in UBS were down 0.3 per cent to $15, Reuters reports, with an official telling the news source the Swiss government - which is currently on hiatus - is due to hold a special meeting to discuss the case today.
Swiss and US authorities have already reached a settlement that will see the names of around 52,000 US clients that hold secret Swiss bank accounts disclosed.
However, according to media in Switzerland, the two countries are yet to agree on how the data will be provided to officials in the US.
It is believed that a deal that would prevent UBS needing to face a tax trial in the US has yet to be reached by the two parties.
A court case that was due to begin last month was delayed after UBS and the US Internal Revenue Services requested extra time to reach an agreement.