Finnair said it is limiting seats on flights between London and Helsinki due to the restrictions set by Heathrow airport in a press release on Wednesday.

London's busiest airport, Heathrow, has said that it will limit the airport's number of passengers due to congestion and staff shortages.

According to Finnair's press release, Heathrow has demanded that airlines limit the number of passengers under the threat of legal action.

The Finnish flag-carrier said that it has to limit seats on the London-Helsinki flights and that it is cancelling the reservations of some customers for flights from 20 to 24 July.

The cancellations affect about 100 customers per day.

The carrier is still operating four flights a day from the British capital.

Those whose flight itineraries have been cancelled can try to find an alternate route through Finnair-though the airline says there are few options. In addition, it is possible to apply for a refund or contact Finnair's customer service.

Finnair will also not take new reservations for London-Helsinki flights until September 11, when the restrictions imposed by the airport are set to expire.

Cancellations on Rome, Paris and Tampere routes, too

Pauliina Palttala from Finnair communications noted that many airports in Europe are now facing challenges in ground services, baggage handling and/or security checks.

According to Palttala, the situation at Helsinki Airport is better that at many European airports, without heavy congestion.

"We're doing our best to find alternative routes for customers, but there are limited flights available due to the restrictions at Heathrow," Palttala told Yle on Thursday.

Finnair has also had to cancel some Rome and Paris flights and replace Tampere flights with buses. Ten departures have been cancelled since last Friday, four of them due to crew shortages. Two of these were domestic Tampere flights.

In addition to cancellations, flights have also been delayed due to other issues such as plane maintenance.