The Council of Trade Unions has started court action in a bid to bring former Pike River Mine manager Peter Whittall to trial.
Shortly before Christmas, all 12 charges against Mr Whittall over the tragedy which killed 29 men were dropped.
The CTU said it would consider a judicial review of that decision.
President Helen Kelly told the Greymouth Star it had filed preliminary proceedings with the Wellington District Court on December 24, seeking more information.
Ms Kelly said it was filed on behalf of a sample of the families, and the first step was to get all the information.