Labour says the decision not to pursue charges against Peter Whittall for breaches of health and safety rules is outrageous.
The Crown decided the chances of a successful prosecution against the chief executive of Pike River Coal over the mine's explosion, in which 29 men died in November 2010, were unlikely.
Whittall and other officers of Pike River Coal are offering $3.4 million to the families now the charges have been dropped.
A lawyer representing Pike River Coal management denies there was any back room deal over a prosecution.
But the Labour MP Andrew Little disagrees, saying there is no question that a deal has been done.
The families of some of the dead men say they are appalled. Bernie Monk, whose son was killed, said the decision is unjust and that he wants investigators to re-enter the mine so evidence can be gathered to lay criminal charges.
He says the decision has put New Zealand justice back a long way.
Morning Report also spoke to the president of the Council of Trade Unions and the Minister of Labour.