Thousands of travelers faced chaos Tuesday after low-cost Spanish airline Vueling cancelled and delayed fights for the sixth consecutive day, local media reported.

More than 76,000 passengers have been affected since the airline began changing flights at Barcelona’s El Prat Airport. On Tuesday, Vueling cancelled 66 flights.

The airline blamed a “strike by French air traffic controllers” but earlier in the week the government launched an investigation into whether the airline, owned by British Airways and Iberia’s parent group IAG, had been overselling flights.

The local Catalan government also said it would consider an investigation.

The chaos coincided with the start of Spain’s peak tourism season, which is widely expected to break records this summer.

The airline could face fines of up to 4.5 million euros ($5 million) and lose its permanent operating license, according to news website El Espanol.

Economy Minister Luis de Guindos told local radio the disruption was due to a “planning problem” by Vueling. He said the airline was “doing a lot of harm to its users and to the image of Spain.”

Vueling was not available for comment but in a statement CEO Javier Sanchez-Prieto said: “I want to apologize to our clients… all of our workers are focused on fixing the situation.”

Jose Antonio Ramirez, a spokesman for airport workers, said staff had been assaulted by angry passengers.