It appears the Government is scared of working people having a say in their workplace, the Council of Trade Unions (CTU) says.
As the legislation stands, company directors and managers could face up to five years in prison and a $3 million fine for recklessly endangering workers.
The Health and Safety Reform Bill, which has passed its first reading in Parliament, would make workplaces responsible for the health and safety of their workers.
The bill was introduced as a result of the disaster at the Pike River Coal Mine.
The Green Party said the Government would be responsible for future workplace deaths if it watered down the new health and safety legislation.
The select committee considering the bill has delayed its report to Parliament by two months after National MPs raised objections, with the main areas of contention understood to be enforcement on farms and whether all provisions should apply to small business.
The backbench revolt in the government caucus appears to have been led by the former minister Judith Collins.
The Greens' workplace health and safety spokesperson, Denise Roche, said Ms Collins' political machinations were putting workers' lives at risk, and that the government had to take responsibility for weakening the legislation.
CTU president Helen Kelly told Morning Report the Government has promised the families of people who have been killed at work that this law will be implemented.
"A small business will benefit from having a trained health and safety rep and will protect themselves against charges of being reckless and not caring about health and safety."