The Swiss federal administrative court has issued a temporary injunction to halt the handover of UBS clients' documents to the US authorities.
The court sent a fax to this effect on Friday evening to the Financial Market Supervisory Authority (Finma) and to eight UBS clients who had appealed to the court against Finma's decision to pass on their documents.
The clients claimed that the handover of the documents would have extremely serious consequences for them. They requested the injunction on the grounds that there was insufficient legal basis for the documents to be given to the US authorities.
The court has asked Finma to give its response to the plaintiffs' claim by next Tuesday.
However, a spokesman for UBS said the documents had already been sent on Wednesday.
After months of pressure, UBS and Finma announced on Thursday the decision to hand over confidential details of 250 clients whom the US authorities suspect of tax evasion. UBS also agreed to pay $780 million (SFr915.8 million) in fines after admitting "improper activities" from some of its employees.
The decision has unleashed a wave of controversy in Switzerland, amid fears that it means the end of Swiss banking secrecy.