The ousted president of Catalonia, Carles Puigdemont, claims Spain has disregarded democracy.
He has been accused by Madrid of rebellion and misusing public funds after the parliament in Barcelona voted for independence.
A protest in Barcelona later will call for the release of jailed separatist leaders ahead of the Catalonia election in December.
Currently in Brussels, Mr Puigdemont is challenging a European Arrest Warrant, and has branded his treatment "a disgrace".
He said: "To be treated like a criminal, like a drug-trafficker, like a paedophile, like a serial killer, I think this is abuse.
"This isn't politics, this is using the courts to do politics."