The concrete company contracted to undertake the sealing of the Pike River mine shaft has pulled out of the job.
Allied Concrete decided not to supply the concrete required to seal the mine at the request of families of the victims, who are fighting to get a mines rescue team into the drift to find any evidence and bodies.
Twenty-nine workers were killed by an explosion in the mine on November 19, 2010.
A statement from Pike River families says Allied has told them it will refuse to supply concrete "until the dispute over re-entering the mine is resolved".
Sonya Rockhouse, whose son Ben was one of the victims, says the families are "incredibly relieved" by the decision.
"We understand this means the sealing of the mine cannot go ahead, and we're grateful to Allied and to all of the Kiwis who have supported us to stop the mine being sealed.
"All we want is the chance to go in and check before our boys and any evidence is sealed away forever."
WorkSafe has issued a notice ordering the mine be permanently sealed by November 30 this year. It has not commented on Allied Concrete's decision.