Catalan politicians and activists accused Spain's top judges of bias during their trial in Madrid on Tuesday for their part in the 2017 independence movement.
Twelve people are accused of rebellion against Spain and misuse of public funds.
Former Catalan President and leader of the separatist movement Carles Puigdemont is not among the 12. He is currently exiled in Belgium.
Mr Puigdemont said he feared a "politicisation of the justice system" in the trial.
The 12 politicians and activists have been in pre-trial detention for over a year. Convictions could result in jail terms of up to 25 years.
Defendants have pleaded their innocence and accused Spain of rolling out a PR war.
The most senior person on trial is the former vice president Oriol Junqueras.
Spanish member of European parliament Antonio Lopez Isturiz said there must be respect for Spain’s constitution by the country’s regional powers.
"We have a clear separation of powers. The rebellion was against the Spanish constitution," the MEP reportedly told the BBC.
“Spain is like a little Europe, we have different nationalities, but we are united by our crown and our constitution.”
He backed the pre-trail detention period that critics have argued has been too long, citing a “risk that they could go out of the country”.
Hitting back at critics accusing Spain of repression, Mr Lopez said Spain was the world’s 19th top “full democracy”, citing the Economist’s Democracy Index. He is not alone in making this particular reference.
Prime Minister Pedro Sanchez and the country’s top judge have used the index as a means to assert their claim of Spain’s functioning democracy.
Catalonia’s government spokesperson Elsa Artadi said the actions of Spain’s federal government were tantamount to rolling back democracy.
“The Spanish government in this process of freedom and liberal, we (the Catalan people) have to walk through repression”.
“What is happening is a violation of the law,” she said.
Spain's government drew up a campaign in response to the separatists in what is increasingly looking like a PR war.
Hollywood actor Richard Gere was part of an official 'real Spain' campaign video.
A vote on independence, organised by Catalonia’s government but deemed illegal by Spain, took place in Catalonia in October 2017.
Barcelona’s parliament later declared victory and an independent Catalonia.
Madrid then stepped in to shut down the local government. Videos circulated on social media accused Spanish police of using a heavy handed approach.
Catalan separatists gained regional power back from Spain’s government in May.
Thousands turned up to Madrid’s streets on Sunday waving Spanish flags in protest against the government’s plan to hold discussions with Catalans.
According to official figures, 16 per cent of Spain’s population live in Catalonia.
The region is responsible for a quarter of Spain’s exports and attracts 20 per cent of Spain’s foreign investment.
