The Rail and Maritime Union says the latest accident at Lyttelton Port in Christchurch can be blamed on a lack of health and safety standards.
A man was injured on Saturday at the city depot yard in Woolston after a falling container crushed the machine he was operating. The latest accident follows two deaths at the South Island port in late 2013.
Rail and Maritime Union organiser John Kerr said on Monday the port has not had a fulltime health and safety manager for more than a year and the increase in accidents reflects this.
"From our perspective, that's totally unacceptable. Nobody should go to work and not come home. Nobody should go to work and be injured. Poor work is potentially dangerous, but the key word there is potentially.
"With the right health and safety systems in place, and the right management and the right cooperation between union and management, there's no need for anybody to get hurt."
Mr Kerr said the city depot is very much the poor cousin of Lyttelton Port and he was told almost 12 months ago by a manager that it "runs on the smell of an oily rag".
"We have had members talk to us about access to training and that kind of thing. There have been a number of near-misses at city depot."
Mr Kerr said a growing workload as a result of the Canterbury earthquakes, poor safety standards and a lack of training are to blame. He said the situation is complicated by the fact that private shipping companies and contractors have their own safety management systems - and that is a recipe for disaster.
"What we would like to see is proper health and safety participation agreement where the management and union would work together on health and safety, where we have a fulltime health and safety manager, and as much of the work that the port does is brought in-house because that facilitates proper systems and proper health and safety."
While not commenting on whether the port has a fulltime heath and safety manager or accusations of insufficient training, operations manager Paul Monk said the company is looking into what went wrong.
"We're obviously always focused on health and safety for our employees. This accident's occurred at our city depot, which is about six kilometres from the port. We will want to make sure we fully investigate this incident and work and WorkSafe New Zealand to make sure we identify what the causes of it were and what we need to do to prevent these sorts of things happening."