Germany's Verdi trade union has called 24-hour strikes at six northern German seaports starting on Monday evening.
The ports affected are Hamburg, Bremerhaven and Bremen, as well as Wilhelmshaven, Emden and Brake in Lower Saxony, all on the North Sea or on rivers flowing into the North Sea.
The strikes are part of ongoing collective bargaining talks for an 8.2% increase in wages for around 11,000 workers as part of an agreement to run for one year.
On Friday, Verdi rejected an offer from employers, after a survey of more than 6,100 workers. The first round of talks began in July.
The employers, represented by the Central Association of German Seaport Operators (ZDS) in Hamburg, presented an offer in the first round and increased it in the second. Among other measures, the ZDS is offering a 5.1% wage increase over a period of 19 months.
Announcing the strikes, Verdi chief negotiator Sylvi Krisch said: "This signal to the employers that we are serious about our wage demands is evidently urgently needed."
Krisch said Verdi was waiting for the ZDS to set a date for a third round of talks.
