The Engineering Printing and Manufacturing Union says companies like Pike River Coal Ltd should be held to a higher standard when it comes to worker safety.
The company was on Thursday found guilty of fundamental health and safety breaches which led to the deaths of 29 men after explosions at the West Coast mine in November 2010.
The court was told there weren't enough gas detectors and there should have been better drainage of methane gas in the mine.
Each of the nine charges proven against the company carries a maximum penalty of $250,000.
However, the union's assistant national secretary, Ged O'Connell, says that's not good enough.
Mr O'Connell told New Zealand's Checkpoint programme the country's accountability regime is non-existent when it comes to corporations taking risks that endanger people.
"When you're endangering people's lives and, in fact, been found to cause their deaths, then there's got to be a regime of accountability.
"And corporate manslaughter seems to be the one that may motivate people to get into action around these things."
Mr O'Connell says the maximum penalty would be just over $2 million, which probably won't be collected.