Spanish Prime Minister Mariano Rajoy is promising to use "all political and legal means" to stop the Catalan region's efforts to become an independent republic.
In a nationally televised speech Tuesday, Rajoy called Catalonia's independence desires "an act of provocation."
"As long as I am the head of the government, Spain will remain a nation of free and equal citizens," he said. "This proposal, in case it is approved by Catalonia's parliament, will not have any effect."
Pro-independence parties won a majority of seats in Catalan regional elections last month. They announced Tuesday that the body would adopt measures next month to begin the process of breaking away from Spain. Backers of the measures say they expect full independence within 18 months.
Catalonia is the area of northeast Spain that includes Barcelona, the regional capital, and a number of popular Mediterranean beach resorts.
The independence movement is more than a century old but recently picked up steam as the Spanish economy struggles to emerge from recession.