Thousands of people are marching in Barcelona, calling for the region to reject independence and stay with Spain.
It comes a week after the Catalan government held a referendum, which was won by the 'Yes' side.
There have been several claims of irregularities with the vote, and many ballot boxes were seized by Spanish police.
These people have gone to the rally in Barcelona to call for unity.
Last night, the Spanish Prime Minister said he may use the constitution to suspend Catalonia's autonomy, if it declares independence.
He's also ruled out calling a snap general election as a result of the crisis - and will keep extra national police there.
Mariano Rajoy had this message for people across the country:
