Parliamentarians from four parties have signed a letter to the Spanish government voicing “grave concern” at a widening crackdown against organisers of the referendum on 1 October, which Spain’s constitutional court has ruled is illegal.
The constitutional row has seen Catalan government officials arrested and control over devolved institutions taken by authorities in Madrid.
At the weekend, Catalan ministers rejected calls from the Spanish interior ministry for “joint coordination” of the Mossos d’Esquadra, the provincial police.
Tens of thousands joined rallies across Catalonia today in support of the vote, which independence campaigners say will go ahead despite ballots being seized by police.
Writing to Spanish Prime Minister Mariano Rajoy as well as political leaders in Catalonia, 18 Holyrood parliamentarians accused in Madrid of flouting “the norms of European democracy”.
Their letter follows Nicola Sturgeon’s call last week for Spain to respect Catalonia’s “right of self-determination”.
Among the signatories are Scottish Liberal Democrat leader Willie Rennie, and representatives from the SNP, Labour and the Greens.
Despite their “collective neutrality” on Catalonia’s future, MSPs say the arrest of Catalan government ministers was “no way for a democratic European state to act against its own people”.
“The Spanish government claim to be acting in defence of democracy but threats of legal action against hundreds of democratically elected representatives and repressive acts against an elected government, media organisations and citizens are in no way democratic acts,” the MSPs say.
“The recent arrest of a Catalan government minister and a number of government staff was a particular violation of the norms of European democracy.
“The situation in Catalonia is a political challenge and it can only be adequately resolved through political action, through dialogue and through allowing the people to express their will democratically.”
Green MSP Ross Greer, who organised the letter, said: “It’s certainly not for us to tell the Catalan people what choices they should make.
“As democrats and parliamentarians however, we must defend the right of peoples across the world to decide their own future and the right of elected representatives to carry out their duties to the people without fear of arrest.”
“To see a state at the heart of Europe take such oppressive actions against its own people is simply unacceptable.”
Twelve Catalan government officials arrested last week have been released, but six remain under investigation.
Ballot papers were handed out at a rally in Barcelona on Sunday. Jordi Cuixart, the president of the separatist group Omnium Cultural, told campaigners: “Here are the packs of ballots that we ask you to hand out across Catalonia.”
Carme Forcadell, the speaker of Catalonia’s regional parliament, told the crowd: “I ask you to go out and vote! Vote for the future of Catalonia!”