ZURICH/PARIS (Reuters) - UBS UBSG.S pledged on Tuesday to appeal against a French ruling not to give it a say in a plea deal by a former employee embroiled in a long-running case over whether the Swiss bank helped wealthy clients avoid taxes.

FILE PHOTO: The offices of Swiss bank UBS are seen in the financial district of the City of London, Britain October 31, 2012. REUTERS/Chris Helgren/File Photo

The court ruling that blocked UBS from contesting the plea deal by a former executive is a setback for UBS, as it could lose one of its witnesses during the trial it faces in France.

“We (UBS France SA) take note of the decision of the Investigation Chamber to not admit the bank as a ‘partie civile’ in the guilty plea proceedings against one of our former employees,” UBS said in an email.

“We will appeal this decision.”

France and other European Union countries have launched a campaign to encourage taxpayers to come clean on previously undeclared assets held abroad, and clamped down on aggressive tax optimization techniques by multinational companies.

UBS has disputed the allegations of wrongdoing.

After settlement negotiations failed, French magistrates ordered that UBS stand trial on charges of aggravated tax fraud and money laundering as well as illegally offering related services, a judicial source has said.

French newspaper JDD said UBS had rejected a 1.1 billion euro ($1.30 billion) settlement proposed by prosecutors.

UBS settled a tax case with German authorities in 2014 for around 300 million euros.

($1 = 0.8470 euros)