The Government is facing questions after footage of a robot entering Pike River Mine was leaked to Newshub.
Opposition politicians are accusing the Government of withholding evidence, and say the footage appears to prove re-entering the mine is not as dangerous as the Government has claimed.
The footage is time-stamped with the date March 15, 2011 - three months after the explosion which killed 29 men.
Bernie Monk, spokesperson for the families of those killed in the explosion, wants to know what else is being withheld from the families.
"I was angry that we'd never been shown it, but I was so angry to know that someone went down so far into the mines," Mr Monk told RadioLIVE's First at Five on Monday.
Dean Dunbar, father of 17-year-old Joseph Dunbar who was killed in the accident, told Newshub the footage demonstrates the "orchestrated pile of crap that been thrown at us for years".
"They made it look and sound explosive. It's not."
Until now, the video had not been seen by the families of those killed.
- Bill English claims he did not know about Pike River robot footage
- Video: Inside the Pike River mine - what police never showed the families
Labour Party leader Andrew Little says the footage fails to support the Government's claim the drift could collapse if it was re-entered.
"The sight of men moving confidently inside the drift with only breathing masks on suggests this isn't the excessively dangerous situation National and Solid Energy portray it as," Mr Little said.
"National claims sending people into the drift would unduly risk their lives. Yet, here is film of two men calmly working in the drift, taking their time to make an ad hoc water cover for a robot."
Mr Little is backed by the Green Party, who say it's shocking Nick Smith, the Acting Minister of Conservation for Pike River, has not seen the footage.
"Nick Smith has confirmed he knew about this video and that he never bothered to watch it. That tells you pretty much everything you need to know about him," said Denise Roche, Green Party spokesperson for workplace relations and safety.
New Zealand First is taking the criticism a step further, saying it shows "there has been a massive cover-up going on" and it is safe to enter the mine.
"Why would you engage in a cover-up unless there was an attempt to avoid seriously material evidence? In short, the question is, is this a crime scene that we are avoiding looking at?" NZ First leader Winston Peters asked on First at Five.
"The Government was in position of ownership of this issue. We are now led to believe on so many other issues that Mr Key didn't know - how many times have you heard that?"
A spokesperson for Dr Smith, however, maintains re-entry is unsafe.
"As we have repeatedly stated, gas levels beyond the seal are consistently around 100 percent methane, making a manned re-entry unsafe."
Mr Little doesn't buy that claim.
"The fact that the robot overheats and emits smoke yet no explosion is triggered makes a lie of Nick Smith's claim that the 98 percent methane atmosphere in the drift is highly flammable," he said.
"In fact, as the scientifically literate Nick Smith surely knows, methane cannot explode in a nearly pure methane atmosphere with little oxygen."