Due to a cyber incident affecting a third-party provider, Canadian airline company Sunwing Airlines has been forced to delay its flights for days, disrupting the plans of thousands of passengers.

Chicago-based Airline Choice is a provider of passenger management software solutions for airlines, airports, and ground handlers. The company confirmed earlier this week that it was hit by a “data security event” on Sunday, which compromised its server networks and disabled its check-in system.

Without Airline Choice’s check-in system, Sunwing staff was forced to manually process flights and fill out boarding passes. However, the system outage led to severely delayed flight schedules, which left many travellers stranded. Notably, Sunwing customers in sun destinations such as the Caribbean, Mexico and Central America were left to fend for themselves due to the delays.

Many of the disgruntled customers have taken to social media to voice their frustration about their delayed departures, and some have also indicated that they had to cancel holiday reservations, Toronto Sun said.

In an email statement to The Canadian Press, Airline Choice explained that it took some of its systems offline as a precaution to secure its environment, and that it has launched an investigation into the matter.

Meanwhile, Sunwing has subcontracted aircraft from other Canadian airlines – which include Air Transat, Nolinor Aviation, and WestJet – to help relieve some of the flight backlog, CBC News reported.

Neither Sunwing nor Airline Choice have provided a timeline for the restoration of the affected systems.