Airberlin has urged striking unions in Berlin to return to the table after tens of thousands of passengers have been prevented from boarding their flights by a continuing wage dispute.

An extension of the strike involving ground handlers at Berlin’s two airports was extended until 5am Wednesday Berlin time and led to the cancellation of about 650 flights on Monday. This was in addition to more than 700 flights cancelled at the two airports, Tegel and Schoenefeld, on Friday.

Ground staff working in areas such check-in, baggage handling and directing aircraft are striking for a pay increase from the companies employing them.

Union are demanding a pay increase to 12 euros ($US12.80) an hour from about 11 euros. The demand was initially met by much lower offers which have since been increased to an 8 percent increase over three years.

Airberlin said it cancelled more than 200 flights on Friday and said hundreds more would be cancelled Monday and Tuesday. 

The only flights operated by the carrier were long-haul services to Abu Dhabi, the Caribbean and the US and Tel Aviv aswell as long-haul feeder flights to the carrier’s hub in Dusseldorf.

“Each day that this labour dispute continues is causing millions in damages to the airline sector and all other service providers at Berlin’s airports,”’ airberlin chief executive. Thomas Winkelmann and Chief human resources officer Martina Niemann said in a letter sent to unions.

“As the largest airline operating from Berlin-Tegel airport, this dispute is hitting airberlin particularly hard. 

"We therefore urge both parties involved in this wage dispute to take responsibility and return to the negotiating table without further delay.”

Among those affected by the strike were visitors to last week’s ITB International Travel Trade Show.