France’s largest air traffic controllers’ union has called for a strike on September 15, which could disrupt traffic at a time when the country expects hundreds of thousands of fans to visit for the Rugby World Cup. 

The SNCTA union said it’s calling the strike in order “to ensure that the inflation rate is caught up with and that mandatory annual negotiations are set up” on salaries.

The planned strike will take place a week into the Rugby World Cup, which France is hosting from September 8 to October 28. The organizers expect 600,000 international visitors for the event. 

Labor action by air traffic controllers not only affects flights to and from France but can also lead to turmoil elsewhere in Europe, causing delays for planes that fly over the country to reach other destinations.

Earlier this year, French air traffic controllers walked out amid protests against pension reform, leading the civil aviation authority to limit the number of flights at Paris’ Orly airport and some regional airports on and off for weeks.