Large business customers will likely be hardest hit as workers in letter sorting centres walk out. Company mailboxes in the German states of Baden-Württenberg, North Rhine-Westfalia and Bavaria are expected to remain empty.
Customers in Rhineland-Palatinate, Saarland, Lower Saxony and Bremen have also been affected by the strike, which began at 10 pm on Sunday in at sorting centres in Duisburg, Wiesbaden and Hamburg.
Employees also stopped work at a sorting centre in the Berlin district of Lichterfelde.
Workers begin voting on Friday on whether to start an unlimited strike.
German Economy Minister Michael Glos told the regional newspaper Neue Osnabrücker Zeitung in its Tuesday addition that a strike is the ‘worst possible alternative'.
“We need a quick settlement,” Glos said, encouraging the company and union to return to the negotiating table.