A key group of service engineers employed at Aberdeen port went on strike yesterday in a dispute over pay.
Workers in Newcastle and Portsmouth are also taking part in the 48 hour industrial action.
The move is understood to involve 12 people across the three locations.
They are employed by global shipping logistics and maintenance outfit MacGregor.
Micky Thompson, regional organiser at the RMT trade union, said workers were unhappy that new terms and conditions had been introduced without consultation.
The changes are understood to have included a 2% pay rise.
MacGregor, a subsidiary of Cargotec, provides cargo and load handling services to the marine and offshore industries.
The company has been contacted for comment.