France's finance minister has offered assistance to one of three French men who have gone on trial in Luxembourg over the leak of documents revealing corporate tax deals, reports the BBC.
Michel Sapin told parliament that Antoine Deltour was "defending the general interest".
Mr Deltour is accused of passing information to a journalist.
The LuxLeaks scandal cast light on how Luxembourg helped giant companies slash their global tax bills.
Mr Deltour and his co-defendants could face up to 10 years in jail.
The government and companies named say their tax practices are not illegal.
It was the biggest leak of its kind until the Panama Papers this year showed how the rich and powerful use tax havens to hide their wealth.
Mr Deltour, a former auditor at PricewaterhouseCoopers (PwC), is accused of passing information on clients to French journalist Edouard Perrin, who first broke the story on French TV in 2012, in collaboration with the BBC's Panorama.
He faces charges of theft, revealing business secrets, violation of professional secrets and money laundering.