Catalonia's president on Saturday formally called a referendum to decide whether Spain's richest region should be independent, defying Madrid which vowed to block the move.
Shortly after Artur Mas set the vote for Nov. 9, the Spanish government said the referendum would not take place because it was "unconstitutional."
Deputy Prime Minister Soraya Saenz de Santamaria warned that no one "was above the national will of the Spanish people."
The government immediately began the process of appealing to the Constitutional Court, which is expected to annul the decree signed by Mas.
The independence movement in Catalonia has gathered strength in recent years.