FRANKFURT - Germany's Munich and Hamburg airports were hit by strikes by public sector union Verdi on Thursday and Friday, with airlines cancelling about 80 percent of flights in Munich.

Munich, Germany's second-largest hub, said in a statement on its website that there was a risk that even more flights could be cancelled and that passengers planning to travel through Munich should contact their airlines.

Verdi has staged several walk-outs in Germany since wage negotiations kicked off in January.

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The union said that staff at Hamburg airport's operator, as well as at services including at maintenance, IT, security and baggage handling would not work during the two days.

German airport association ADV said that the strikes, as well as similar airport walk-outs in Duesseldorf and Cologne earlier this week, were disrupting travel plans of almost 300,000 passengers.

"Two-day strikes that cut off German metropolitan regions from international air travel go far beyond what could qualify as token strikes," ADV said.