Rail and Maritime Union members are still refusing to work overtime at Lyttelton Port, claiming working conditions are unsafe.

The overtime ban is indefinite and the port had to close down operations from midnight last night until 6am.

Rail and Maritime Transport Union branch secretary, Libi Carr says it seems utterly bizzare the port has rejected claims from workers.

"All we want is to bring industrial relations of the Port into the 21st century by engaging constructively with LPC around productivity, efficiency and safety and having our members treated equitably."

Ms Carr says there's a moral and legal obligation from the company to address these issues especially with it's track record of deaths and injuries.

"Part of wanting to engage with the company around health and safety is to make sure that this doesn't happen again, because no worker should go to work and wonder if they're going home safely at night."