The former Catalan leader, Artur Mas is to be prosecuted over the 2014 independence referendum, facing charges of "serious disobedience" and "malfeasance".
The decision, announced by Catalan's High Court on Thursday, accuses Mr Mas of organising the referendum despite Spain's Constitutional Court imposing an injuction on it.
If found guilty, Mr Mas will be prohibited from holding public office for 10 years.