Dispute over pay, conditions
"Preparations for open-ended strikes are in full swing," he said.
Staff at Deutsche Post have staged a series of strikes since the company announced plans in January to create 10,000 new jobs at its parcel business by 2020 that would come with lower wages than those of other group employees.
Verdi has said such a move breaches an agreement limiting how much business Deutsche Post can outsource. The union said it would only accept it if the company shortened the working hours of 140,000 employees and raised wages by 5.5 per cent.
Earlier this week, Verdi offered to scrap its demand for the wage increase as long as workers at the new parcel units were paid the same as employees at the rest of the group.
Deutsche Post provisionally rejected the offer but has said it would give a full response early next week.