The Restoration implemented harsh measures to repress the Catalan workers' movement, which did not recover until the 1880s. In 1881, Catalan syndicalists constituted the Spanish Regional Workers' Federation. The UGT (General Workers' Union) was founded in Barcelona in 1888 but apart from in Mataró and Reus was not popular amongst the Catalan working class, who inclined towards organisations that were libertarian in outlook. International Labour Day was celebrated for the first time on 1 May 1890. At the end of the century, anarchists initiated a campaign of terrorism that was individualist in nature, resulting in bloody attacks such as the one at the Liceu opera house in 1893.