The ruling is a fresh blow to the government of the wealthy northeastern Spanish region after Spain's Constitutional Court last month quashed a resolution by the regional parliament calling for a referendum this year.
Separatists in Catalonia have for years tried to win approval from Spain's central government for an independence vote like Scotland's 2014 referendum on independence from Britain, which resulted in a "no" vote.
The Catalan government is committed to holding a referendum with or without Madrid's permission by September.
The government's top legal advisory body, the Council for Statutory Guarantees, said Friday the regional government "does not have the authority to... call a vote on the political future of Catalonia".
The competence, it said, lies exclusively with the Spanish state.
The panel has only advisory functions but acts as a constitutional court for the region.
Its ruling was unanimous, even though half of the eight members were appointed by separatist parties.
Anti-independence parties had asked the council for an opinion on the region's 2017 budget, which includes provisions for a referendum promised by Catalan President Carles Puigdemont.
As the court's opinion is non-binding, the regional parliament must now decide whether to remove this line from the budget.
Catalonia's former president, Artur Mas, tried to hold an independence referendum, which was also banned by the court.
He countered by calling a symbolic, non-binding independence vote. This too was stopped by the court.
But in November 2014 Mas went ahead anyway. More than 80 percent of those who cast a ballot chose independence, but just 2.3 million out of 6.3 million eligible voters took part.
Catalonia's long-standing demands for greater autonomy have been exacerbated by Spain's economic downturn, with many Catalans resenting the taxes they pay to the central government in Madrid to subsidise poorer regions.
Calls for outright independence have increased in recent years. Polls show that Catalonia, which accounts for almost a fifth of Spain's economic output, is roughly split in half over breaking away.