The High Court has declined an appeal to review the decision not to prosecute Pike River Mine boss Peter Whittall.

The review was sought by Worksafe and two family members of the 29 miners who died in the mine explosion five years ago.

The Council of Trade Union says its extremely concerned about the decision. President Richard Wagstaff says the prosecution against Peter Whittall did not go ahead after his insurers paid 1.4 million dollars to the court as an alternative.

He says no one has ever been held accountable for the deaths. Mr Wagstaff says the CTU supported the Pike River families who sought to pursue justice and the union is now considering appealing this decision.