France on Wednesday launched an official investigation into the French subsidiary of Swiss banking giant USB for alleged witness intimidation, a source close to the case told AFP.

UBS France is suspected of trying to silence a whistle-blower who was behind revelations of alleged tax fraud by the bank, the source said.

The French subsidiary was also designated an “assisted witness” on a charge of moral harassment, a status between a full witness and being put under formal investigation.

Statements by a former internal audit official at UBS France contributed to revealing the affair, which led to a formal investigation into the Swiss parent bank for money-laundering and tax fraud, and for complicity at UBS France.

Wednesday’s French legal action came less than two weeks after the end of the formal investigation stage of that probe.

UBS is alleged to have set up between 2004 and 2012 a system to incite rich French clients to open bank accounts in Switzerland to avoid paying tax in their home country.

A spokesman for UBS France was not immediately available.

On Friday Belgium charged UBS with “serious and organised” fiscal fraud for encouraging clients to cheat on their taxes, as well as being involved in money laundering.