Spain’s constitutional court on Thursday suspended a Parliament session that Catalonia had planned for Monday possibly to declare independence, BBC reported.

Catalonia’s Socialist Party, which opposes secession, had challenged the Parliament session. The court upheld the challenge, and said allowing Parliament to meet and declare independence would violate the rights of the Socialist Party’s MPs.

Earlier in the day, Spanish Prime Minister Mariano Rajoy warned that the situation could escalate further if the Catalans went ahead to declare independence. Rajoy told Spanish news agency Efe that the best solution to avoid greater harm would be “return to legality”, and confirm soon that there won’t be a unilateral independence declaration. His comments came a day after Catalan leader Carles Puigdemont said the autonomous region would declare independence from Spain in a “matter of days”.

A referendum was held on Sunday despite being declared illegal by Madrid. It saw more than 90.9% voters backing the call for independence. Over 900 people were injured in the violence during voting, as Spanish police attempted to block the process.