LONDON — Hundreds of flights have been canceled across Germany as airport workers stage a nationwide strike over pay, posing a major disruption for air travelers.

The industrial action, led by the trade union Verdi, began unexpectedly on Sunday at Hamburg Airport, before expanding to a nationwide strike.

Passengers at Frankfurt, Munich, Berlin and other major hubs have been urged not to travel to airports, with operations severely disrupted. Frankfurt, Germany's busiest airport, said passengers would be unable to board flights and transfer would "almost certainly" be affected.

Verdi, which represents public sector and transport workers, is in an ongoing dispute over wages and working conditions.

German media reports thousands of flights could be canceled across the day, disrupting travel for more than 500,000 passengers.

Lufthansa, whose main hub is in Frankfurt, confirmed "delays and extensive cancellations" across all its airlines, while Munich Airport warned of a "greatly reduced flight schedule."

Katja Bromm, spokeswoman for Hamburg Airport, where all 143 departures scheduled on Monday have already been cancelled, said Verdi was "dishonorable" to call a strike without notice at the start of the holiday season.

She said that Sunday's walkouts were "excessive and unfair to tens of thousands of travelers who have nothing to do with the disputes".

A spokesman for Verdi accepted that the strike would affect many, but told German media that causing disruption was necessary to extract a better offer from employers.

Many of Frankfurt Airport's 1,770 scheduled flights have already been canceled, while the majority of Munich's 820 flights are expected to be canceled.

Hundreds more cancellations are anticipated across Stuttgart, Dusseldorf, Cologne and Berlin.

Many passengers had already checked in their luggage and were having problems getting it returned, according to public broadcaster NDR. It also reports that the strike has brought air traffic at Hanover Airport to a standstill.

Beyond airports, Verdi has also called for strikes in waste collection across several German cities, including Berlin, Essen and Kiel, where bins have gone unemptied since last week.

The union is demanding an 8% pay increase for airport workers, or at least €350 more per month, along with higher bonuses and extra time off. Employers have so far rejected these demands as unaffordable.

Further strikes were expected to go ahead this week in facilities operated by the federal government and local authorities, news agency DPA reported, citing a Verdi spokesperson.

The next round of talks is set to take place on Friday in Potsdam. — BBC