Pilots at the French national airline have started a four-day strike that could disrupt plans for thousands of football fans on the second day of the Euro 2016 competition.
Air France has cancelled up to 30% of its flights on Saturday.
But it said it would prioritise journeys to cities that were hosting tournament matches.
The pilots' union wants the government to scrap new labour laws that will make it easier to hire and fire people.
It is one of many unions taking action - rubbish will not be collected in Paris until Wednesday, train services have only recently resumed after a nine-day strike, and at the end of last month petrol stations ran dry when protesters blockaded oil refineries.
President Francois Hollande has warned unions against disrupting the tournament.
He said: "I appeal to everyone's sense of responsibility because if the state must do its duty - and it will, it will take all the measures that are necessary.
"At the same time, it is also necessary that those who are taking part in actions, or who are organising them should also shoulder their responsibility... so that this great event can be a shared popular festival."
The pilots' union Spaf (Syndicat des Pilotes d'Air France) says its strike will run from Saturday until Tuesday.
But the company's chief executive, Frederic Gagey, promised to try and minimise disruption to host cities.
He said: "Of course we will look after the Euro tournament."
He added that the dispute would cost the airline €5m (£3.9m) a day.
In all, seven million people are expected to visit the 10 French cities where matches are taking place.
