Hundreds of thousands of people have led a protest march in Barcelona, the capital of Spain’s semi-autonomous Catalonia region, against a campaign for independence of the region from the mainland.

Around 350,000 people took part in the rally in central Barcelona on Sunday, municipal police said. Organizers, however, put the turnout at 930,000 to 950,000. 

“Catalonia is Spain” and “Together we are stronger” could be read on banners carried by protesters, who waved Spanish and Catalan flags.

On Monday, Catalonia’s parliament is set to declare independence from Madrid based on the results of a controversial referendum last week, which was held amid unprecedented tension on the streets of Catalonia. The constitutional court in Madrid has ruled that the Monday parliament session must be suspended. Madrid says the entire independence campaign, including the referendum itself, was illegal.

Spain’s central government has also issued repeated warnings that declaring independence would have dire consequences for the region and the secessionist authorities.

Those who marched to oppose independence in Barcelona on Sunday said they wanted to remain part of Spain.

“We are facing a tremendous unknown. We will see what happens this week, but we have to speak out very loudly so they know what we want,” said a 72-year-old demonstrator, adding, “We feel both Catalan and Spanish.”

The anti-independence group, the Catalan Civil Society, organized the march under the slogan, “Let’s recover our senses.” The group’s main aim has been declared to mobilize a “silent majority” of citizens in Catalonia who oppose independence.

Some 2.3 million people cast their ballots in the October 1 referendum, representing only 43 percent of Catalonia’s 5.3 million eligible voters. The regional government says a yes vote by 90 percent of those who voted is enough to declare independence regardless of the turnout.