SPAIN will seek to block in the courts a watered-down version of a Catalan vote on independence planned for November 9 in the same way it stopped a non-binding referendum, Deputy Prime Minister Soraya Saenz de Santamaria has said.

Tensions have risen between Spain's central government and Catalonia as Madrid blocks all attempts by the region to vote on its future. Madrid argues such a ballot would violate the constitution because it would allow some Spaniards to vote on a matter affecting the whole country.

Ms Saenz de Santamaria said the central government would seek to block the watered-down vote, couched as a "consultation of citizens", to protect the rights of Catalan civil servants so they wouldn't be forced to break the law.

Catalan head Artur Mas plans to hold the ballot, marshalled by volunteers, in place of a non-binding referendum on independence declared illegal by the Constitutional Court.

On Thursday, the highest-ranking state adviser backed a veto of the new consultation, saying it was just as illegal as the original plan.

The government has now asked the Constitutional Court to rule on the legality of the vote. Prime Minister Mariano Rajoy has referred to the consultation as a "pseudo vote".

It is unclear how Madrid would enforce a block on the vote if Catalan leaders decide to press ahead.