PARIS — A Swiss court said Friday that the country’s financial regulator had broken the law when it ordered UBS to hand over data on nearly 300 clients suspected of evading taxes to U.S. authorities a year ago.

The Federal Administrative Court in Bern said that the Swiss Financial Market Supervisory Authority, known as Finma, had gone beyond its mandate.

The regulator argued that its actions last February were justified by laws allowing it to take unspecified preventive measures if banks were threatened with insolvency. But in a 60-page ruling, the judges said the government and the parliament are the only institutions with the authority to implement state of emergency laws.

The agency said it has not decided if it will appeal the ruling to the Swiss Supreme Court. While it is far too late to halt the transmission of certain clients’ data, it could influence the course of future cases, as Switzerland remains embroiled in disputes around tax evasion, namely with France.