2017 Catalan independence referendum

An independence referendum was held on 1 October 2017 in the Spanish autonomous community of Catalonia, passed by the Parliament of Catalonia as the Law on the Referendum on Self-determination of Catalonia and called by the Generalitat de Catalunya. The referendum, known in the Spanish media by the numeronym 1-O (for "1 October"), was declared unconstitutional on 7 September 2017 and suspended by the Constitutional Court of Spain after a request from the Spanish government, who declared it a breach of the Spanish Constitution.

Source: Wikipedia — 2017 Catalan independence referendum (CC BY-SA 4.0)