Employees have brought Germany's two biggest container hubs to a standstill, with workers at a third port set to join them. 

The trade union Verdi wants to force employers to make further concessions in pay talks with the Central Association of German Seaport Operators.

Negotiations for a new collective agreement for the 11,500 German North Sea port employees began in May.

The union has demanded significantly better wages, especially for the lower pay groups, with an hourly wage increase of 3 euro plus a shift allowance increase for working unsocial hours.

It says the increases are vital for workers at the lower end of the pay spectrum.