Spain’s Constitutional Court struck down a Catalan claim to sovereignty in a ruling that threatens to aggravate tensions between the central government and the region’s secessionist movement.

The court in Madrid struck down a resolution approved in January by the Catalan parliament in Barcelona claiming sovereignty for the region as the basis for calling a referendum on independence from Spain. That claim should be considered “unconstitutional and void,” the court said in a ruling distributed by e-mail last night.

Catalan President Artur Mas is pressing ahead with plans for a November referendum to decide whether to secede from Spain, defying Prime Minister Mariano Rajoy who insists such a vote would be illegal. Catalonia accounts for a fifth of the Spanish economy and is home to some of Spain’s biggest companies including Gas Natural SDG SA and CaixaBank SA.

Sovereignty is “not contemplated in our constitution for nationalities and regions that make up the state” and no one can break the principle of the “indissoluble unity of the Spanish Nation,” the ruling said.

The Spanish situation differs from that in Scotland, where the nationalist government in Edinburgh will hold an independence referendum on Sept. 18 with the agreement of the U.K. government in London. Polls show the “No” campaign supported by Prime Minister David Cameron and the main opposition Labour Party ahead of the “Yes” camp led by Scottish First Minister Alex Salmond.

Mas, speaking in the Catalan parliament today, described the constitutional court’s ruling as “serious” and said he would push on with the process of holding a referendum on the region’s sovereignty, the Spanish news service EFE reported.

The regional parliament’s assertion that the Catalan people have the “right to decide” whether to secede could potentially fit within the constitution, depending on how it is interpreted, the court said in a unanimous ruling.