Catalonia's pro-independence executive has insisted on holding the referendum in a move strongly opposed by the central government which says it is illegal.
"We need to prepare for a strategy of tension implemented by the regional government and pro-independence parties," Deputy Prime Minister Soraya Saenz de Santamaria said in a television interview.
"They are looking to provoke and they are looking for the state to react," said Saenz de Santamaria, who is in charge of negotiations on the matter.
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Catalonia, a wealthy region of 7.5 million people, is fiercely proud of its language and customs and has long demanded greater autonomy from Madrid.
For years, separatist politicians in the region have vainly tried to win approval from Spain's central government to hold a vote similar to Scotland's 2014 independence referendum -- which had the approval of the British government.
And while Catalans are divided on the issue, with 48.5 percent against independence and 44.3 percent in favour according to the latest regional government poll, close to three-quarters support holding a referendum.
In February, the Constitutional Court ruled against the planned vote and warned Catalan leaders they faced repercussions if they continued with their project.
Regional authorities face a host of challenges just to hold the referendum without Madrid's consent, and the issue has put civil servants in Catalonia -- who are needed to help organise the vote -- in a delicate situation.
If they disobey orders from their Catalan bosses, they could face disciplinary sanctions.
But if they obey, they will go against Spanish law and also face sanctions, which may even entail losing their jobs.
"You can disobey and assume the consequences," Saenz de Santamaria said.
"But what you can't do is force civil servants trying to do their job as best they can to break the law."