It says even if the decision had been shown to be unlawful, it would not have been set aside as payment had already been made to the families.
The Court of Appeal decision is being blasted as "cheque book justice" by the CTU.
President Richard Wagstaff said victims and families were left out in the cold by the ruling.
"WorkSafe allowed an unrepentant defendant to get his insurer to make a payment to the victims, in return for WorkSafe dropping the charge.
"The Court of Appeal did not think the victims ought to have been consulted before the deal was struck.
"We now need to consider what options remain.
"One thing is for sure the 29 men that were killed on the 19th November 2010 are still no closer to justice."