Ryanair cabin crew based in Spain reportedly walked out on Thursday (30 June), which is likely to cause disruption in Madrid, Malaga, Barcelona, Alicante, Sevilla, Palma, Valencia, Girona, Santiago de Compostela and Ibiza.
Meanwhile, easyJet staff in Spain are said to be preparing to strike for nine days from Friday (1 July).
According to The Telegraph, it comes after Ryanair staff in Belgium, Portugal, France, Italy and Spain staged walkouts last weekend.