The Council of Trade Unions (CTU) is seeking prosecutions against two forestry companies after two workers were killed last year.
Work Safe New Zealand has the first right to prosecute for workplace deaths, and once they have started legal action no one else can.
CTU president Helen Kelly said Work Safe has pursued very few prosecutions after deaths in the forestry industry.
"The government is very reluctant to use their legal powers.
"If they're not going to, we will. It's very important for these two families and for these two men.''
Thirty-two people have been killed in the forestry industry since 2008.
The CTU is seeking leave to launch prosecutions against the forestry companies employing two workers who died at work last year in the central North Island.
Eramiha Pairama, 19, died after being struck by a log in a forest near Whakatane in January 2013 and Charles Finlay, 45, died after being struck on his head by a log in a forest near Tokoroa in July 2013.
Ms Kelly said she did not know all the details of the case but was confident a prosecution would go ahead once the permission to prosecute has been granted by the court.
"We know what we know from talking to families and other people and we believe there's a case.''
Coronial inquests were due to begin next month into eight deaths in the forestry industry, but some hearings are on hold to allow for possible court action.