Catalonian separatist politicians are attempting to hold a referendum to secede from Spain, and the Spanish government is clamping down on this effort, with federal police having arrested several of these politicians, and taking control of some of the region's finances to prevent government monies from being used to carry out the vote which the government deems as illegal. These forcible measures have provoked outcries from pro-independence Catalonians, and demonstrations have formed in the streets in opposition to the government's reaction. Polls show that pro-independence Catalonians are a slight minority, but these measures taken by Spain's conservative government are counterproductive to its ends of preserving the union, and the Catalonian secessionists vow to continue their efforts to carry out the vote. I don't remember the UK dealing with the Scottish separatists in this manner when they passed their secession referendum a few years ago.
That's because the UK granted Scotland permission to hold that vote, and agreed to abide by the result. The Catalonian separatists do not have the permission of the national government, so the government is cracking down.