Albert Rivera, the leader of Spanish nationalist and unionist Ciudadanos (Cs), is willing to discuss the illegalization of CUP, a far-left party that is instrumental in securing a pro-independence majority in the Catalan parliament. In an interview with the Spanish public radio, Rivera sided with Pablo Casado, the head of the conservative People’s Party (PP) in Spain, who said on Wednesday that CUP could be made illegal for endorsing pro-independence grassroots groups that he deemed as “violent.”

Casado proposed using the same law that served in 2003 to ban Batasuna, which Spanish courts ruled as the political arm of the Basque terrorist group ETA. Not only did Rivera back Casado, but he also proposed reforming electoral laws to set a 3% threshold for parties to enter the Spanish Congress—a percentage that would leave out Esquerra (ERC) and PDeCAT, the two main pro-independence parties in Catalonia.

As PP and Cs fall short of the parliamentary majority needed to pass such legislation, Rivera also reached out to Pedro Sánchez, the Spanish president and the leader of the Socialist party.

CUP has repeatedly committed itself to civil disobedience and peaceful protest as a means to achieve independence.