Workers at recycling sites in West Yorkshire struck on Wednesday of last week over allegations of bullying and intimidation by managing company Sita.
Sita controls the borough’s recycling sites on behalf of Kirklees council.
The strike was sparked after one worker at a Kirklees depot claimed he had been locked in an office by his manager.
The workers’ union, Unite, says one manager has made clear that one of his aims is to break the union at Kirklees.
Another day of strikes was planned but has been postponed for talks.