Labour, United Future, The Maori Party, and the Green party all signed an agreement with Pike River families on Tuesday afternoon to re-enter the drift of the Pike River mine where 29 men were killed in an explosion in 2010.
The parties have made a commitment to the Pike River families to re-enter the mine drift and retake ownership of the mine by 2018 - if a new Government is formed after the election.
New Zealand First had already made a previous commitment to re-enter the mine.
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The agreement sets out that if a new Government is formed, the parties "Will act immediately to safely re-enter, fully recover, make safe and comprehensively investigate the Pike River mine drift."
The Government would create a ministerial position for Pike River, establish a Pike River re-entry agency to take ownership of the mine within the first 100 days of Government, and set up a plan to re-enter the mine drift by the end of 2018.
"The purpose of re-entry will be the recovery of human remains, collection of evidence about the disaster to improve future workplace safety, discovery and investigation of any new evidence into causes of the disaster, and to refer evidence of any potential criminality to police for investigation and prosecution if appropriate," the agreement states.
Labour leader Jacinda Ardern said the re-entry of the drift would allow for some of the men to be recovered, and for evidence to be gathered about the cause of the explosions.
"I cannot imagine having my family member in that mine and not coming home," Ms Ardern said.
"Returning your men and your boys is as much about a personal perspective as it is about anything else."
She said that more and more footage is coming out suggesting that New Zealanders don't have the full story about what happened.
Green leader James Shaw said to the families "It is a tribute to you that it has gotten to the point where a majority of the parties in Parliament are prepared to sign up to this pledge.
I acknowledge that the company was never held to account, and that you've never had any basic acknowledgement from the Government or from the company for the stance that you've taken."
Pike River widow Anna Osborne said "This is a huge victory for justice and an enormous step towards getting our boys out, getting the truth, and coming to terms with what happened at Pike River."
Bernie Monk, who lost his son Michael in the mine, said the families will remember the signing of the agreement for the rest of their lives as "a moment when right won out".
"It's nearly seven years since we lost our boys in that awful place, and it's never been properly investigated. With this historic commitment the job of getting into the drift, recovering our boys, and finding evidence of what happened all those years ago is closer than it has ever been."
Sonya Rockhouse lost her son Ben in the mine and her son Daniel was one of the two survivors. She said the families were close to being defeated, but the signing of the agreement has given hope.
"I can't stop thinking about how far we've come since late last year when we started our last-ditch protest at the Pike River road in the middle of nowhere. It was so close to being over, another few days and the mine would have been sealed and given to DOC and we would never have stood a chance of getting in there and finding the truth.
"To be standing in Parliament less than a year later and watching leader after leader signing up to recover the drift, it's just mind-blowing. It's restored my faith in our democracy."
Prime Minister Bill English didn't sign the agreement and said it doesn't make the mine any safer.
"We're working on a plan for unmanned entry which we hope will occur before the end of the year. That will provide a better picture of what's going on in there and then further decisions can be made after that," he said.