An indefinite strike by air traffic controllers employed by Saerco (a private air navigation management company operating at nine Spanish airports) began in the early hours of 17 April, causing significant disruption to flights, particularly at Seville. The stoppage, called by unions USCA and CCOO on behalf of 104 workers, coincides with the Copa del Rey football final between Atlético de Madrid and Real Sociedad, for which around 50 extra flights had been scheduled, as well as the start of Seville's famous Feria de Abril fair on Monday. Unions cite chronic understaffing, deteriorating working conditions, abusive use of on-call arrangements, and safety concerns as the reasons for the action, while Spain's transport ministry has set minimum service levels ranging from 34% to 100% depending on route type, and passenger rights groups are reminding affected travellers of their entitlement to full refunds or rebooking under EU Regulation 261/2004.