It has been reported that up to 500 flights are at risk of cancellation, while and trains, ferries, city metros and buses are all also likely to be affected.

Cabin crew operations for TAP Air Portugal, and its regional providers Portugália and SATA, will suffer up to 79% staff absence, according to Travel Tomorrow. Other airlines are also expecting staffing disruptions.

Staff shortages could create problems at the start of the summer season for Europe’s largest airline by passenger numbers, Ryanair and rival easyJet.

Both airlines fly out of Portuguese hubs.

Airlines are generally obliged to assist or compensate customers if their flight is delayed or cancelled due to a strike and the nature thereof.

It does, however, depend on the conditions of the airline, with some not covering strikes out of their control. This would include airport or baggage handler strikes.

Compensation also depends on the extent of a customer's travel insurance.

This information should be easily accessible on the airline or insurer's website.

Booking a flight for a period when a strike action is known means travellers are unlikely to receive compensation.

Travellers are advised to check for any strikes by their intended airline, departure and arrival airports.

Strikes are primarily used as bargaining chips in negotiations between unions and employers. The possibility remains that both sides will come to an agreement before a strike occurs.