Airlines cannot use strikes as an excuse not to pay compensation to travellers they bump off flights, Europe's highest court has said.

This has widened the scope of passenger rights in the European Union.

Judges at the Luxembourg-based EU Court of Justice (ECJ) said compensation should be extended to passengers affected by unforeseen events beyond the usual causes such as overbooking, long delays and cancellations.

"An air carrier must compensate passengers when they have been denied boarding because their flight was rescheduled as a result of a strike at the airport two days beforehand," the court said in a statement.

Under EU rules, travellers on flights starting or ending in the European Union are entitled to up to €600 for being bumped off. Until now, strikes had not been considered grounds for compensation.

The court said airlines could not cite extraordinary circumstances such as a strike to avoid paying compensation.

The court was ruling on a 2006 incident where Finnish carrier Finnair removed some passengers on a flight from Barcelona to Helsinki to make room for travellers from an earlier flight that had been cancelled.

Finnair did not compensate the passengers.

One of the passengers later went to a Finnish court to seek compensation from Finnair. Judges asked the ECJ for guidance.

The ECJ also said airlines could seek compensation from third parties whose actions had resulted in them bumping off passengers.