A two-day strike by workers at Germany's largest port in Hamburg started Tuesday.
Trade union verdi called the action to increase pressure in ongoing wage negotiations, verdi said in Berlin on Monday.
A larger demonstration through the city is planned for Wednesday, according to the union.
Verdi has been negotiating with employers over an increase in hourly wages as well as a corresponding increase in shift allowances, among other things.
The union is demanding an additional 3 euros ($3.2) per hour, to be paid retroactively from June 1, according to Germen news agency (dpa).
"We were still very much apart in the third round of negotiations," Verdi chief negotiator Maren Ulbrich said, describing an offer presented by employers as unacceptable.
The rise in inflation seen in the past couple of years has hit the lower income groups particularly hard, she said.
A fourth round of negotiations between the union and the Central Association of German Seaport Companies (ZDS) is scheduled for July 11-12.
The latest action comes after workers at several northern German seaports went on strike last month to ramp up the pressure on employers as they entered the third round of talks over pay.
