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.''