High, clear and without nuances: the owner of a cinema or the company that manages it can NOT prevent you from entering the room to watch a movie with a food that you carry with you. If the cinemas allow to eat snacks, snacks and popcorn to the spectators, it does not matter the origin of these. Although the rooms try to transmit messages that suggest their prohibition, there is no legislation that endorses it. In fact, a spectator who attended a movie in a cinema owned by Cinesa who tried to prevent him from entering with popcorn claimed Consumo, and the film company was sanctioned and fined 6,000 euros.
And that despite the fact that at the entrance of these cinemas the following sign bore: "If when you go to dinner at a restaurant you do not take the wine from home, why do you bring popcorn to the movies?". But the legal reality is very different, and the prohibition of straining food alien to the establishment lacks legality. If the screening rooms allow people to eat inside what they sell -at prohibitive prices almost always-, they can not prevent food or drinks from being introduced from abroad, since there is no logical relationship between the economic activity developed in the establishment -the exhibition of films- and the reason why something is prohibited according to the place where it was acquired. Another different case would be that a cinema establishes among its conditions of admission the absolute prohibition of eating, drinking, opening bags of candy or making noises at risk of expulsion.