Five Norwegian airports were shut down by a strike early Friday when 220 union members walked out after all-night contract talks failed to reach a settlement with the national airport authority Avinor.

The strike stranded an estimated 17,000 passengers a day before Norway's May 17 Constitution Day, when thousands of people fly home to join parades and celebrations.

''Avinor strongly regrets the consequences a strike will have for airlines and passengers. Our community and financial considerations made it impossible to meet the demands from the employee representatives,'' said Avinor Chief Executive Sverre Quale.

The strike called by the Norwegian Confederation of Trade Unions shut down the airport in Norway's second-largest city, Bergen, as well as in the towns of Molde, Harstad, Mo i Rana and Moesjoen.

The union, which is Norway's largest, said the negotiations collapsed over demands for wage increases to bring the striking workers to the same pay level as other Avinor staff, and well as over increased shift differentials.

''Our members have for many years felt like a B-Team in Avinor,'' said Lise Olsen, the union's chief negotiator.

Norway's main airport, Gardermoen Airport-Oslo, said the strike had little affect on the capital city's airport apart from flights that had been scheduled to fly to the closed airports.

The union said it would begin expanding the strike to other airports if a settlement is not reached by Sunday.

Avinor is a government-owned company that owns and operates 46 airports in Norway.