The leader of Alianza Nacional (National Alliance), Pedro Pablo Peña, made the comments during a neo-Nazi rally held in Barcelona on Spain's October 12th National Day 2013.
"Catalonia won't become independent without a lot of blood being spilled," he is reported to have said in a speech during the demonstration which saw the group's members carrying banners calling for Catalonia's regional president Artur Mas to be sent to the gas chambers.
Catalan leaders are pushing for a November 9th referendum on the issue of independence for the region with 7.5 million people. Many in Catalonia feel they would be better off without Spain, saying they feel short-changed by the central government which redistributes their taxes.
But the far-right Alianza Nacional, which is anti-immigrant and anti-gay marriage, believes the region is an essential part of Spanish territory.
On Wednesday, an unrepentant Peña refused to back down over his 2013 comments, Spain's 20 minutos newspaper reported.
He is now on trial for charges of inciting hatred and discrimination.
The leader of Spain's far-right Falange group had also been summonsed to appear in court on the same charges on Wednesday but failed to show.
He did, however, answer questions from Madrid. During that declaration he said the "Spanish people" could legitimately use violence if the government failed to prevent the independence of Catalona.
The Falange leader, however, refused to answer questions relating to charges of inciting hatred and violence.