Catalan leader Artur Mas warned that any move by Spain to disrupt today's symbolic and much-disputed vote on independence in the wealthy region would be "a direct attack on democracy".
Spain's Constitutional Court this week ordered the Catalan government to suspend the vote. But Catalonia's nationalist government has vowed to press ahead with the ballot, which will be organised by volunteers without an official electoral roll.
Mas yesterday issued a fresh warning to Madrid, less than 24 hours before the vote was set to go ahead.
"I don't know what they will do, it does not depend on us, but if they have a minimum of common sense I think any action out of the ordinary (to prevent the vote) would be a direct attack on democracy and a direct attack on fundamental rights," Mas said during an interview with public television.
The Spanish government has not specified what legal consequences Catalan leaders, poll workers and voters might face.
But the central government representative in Catalonia has warned the Catalan officials that they cannot use public resources to carry out the ballot.
Spain's conservative Prime Minister Mariano Rajoy says his country cannot hold an independence referendum like Scotland because, unlike Britain, it has a written constitution that forbids it.
But Catalans have pushed ahead defiantly, fired up by Scotland's independence referendum in September, even though Scots voted not to break away from Britain.
Rajoy downplayed the importance of the vote during a speech to supporters of his conservative Popular Party in the eastern city of Caceres.
"What will take place tomorrow, we can call it whatever one wants, but it is not a referendum, not a consultation, nor anything that resembles it, I can't even qualify it. What is certain is that it will not have any effect," he said.
Ballot boxes started being set up at schools and town halls across Catalonia and final rallies and concerts were held to encourage Catalans to turn out and vote.
"Call your parents, your friends and your neighbours and tell them that they have to vote," said Murial Casal, the president of Omnium Cultural, a civil society organisation set up to promote the Catalan language and culture which backs independence, a rally late on Friday.
Mas announced the symbolic vote after the Constitutional Court in September suspended earlier plans for a non-binding, official referendum on secession.
In both its rulings the Constitutional Court ordered Catalonia to suspend its plans for a vote while the court studies its legality.
Catalan officials argue the symbolic vote, which they call a "citizen participation process", is legal.
A delegation of eight lawmakers from across Europe plans to visit over 30 polling stations to verify that voting is "transparent and fair".
