SkyCity says WorkSafe and three independent investigations have deemed air quality safe for workers to return.
Staff went on strike on Friday when the company opened for the first time since Tuesday's mega blaze at the International Convention Centre, which sent smoke billowing across the CBD for days.
But SkyCity says air quality has been rigorously monitored, showing no level of threat at any stage since it reopened for business.
"This includes eight external occupational hygienists working under the supervision of one of NZ's leading occupational hygienists, Derek Miller," a spokesperson told Newshub.
"WorkSafe have also visited SkyCity Auckland and have undertaken observations and are satisfied that SkyCity have taken appropriate actions to manage any potential health related risks."
- Photos reveal extent of blaze's damage
- Casino back in business, hotel and tower set to reopen Friday
- More SkyCity workers, customers criticise the company's response to the emergency
The conglomerate says the strike involved only 46 of its 1389 staff, and there no complaints from customers.
Unite union, which represents many workers at the casino, has criticised the company for not evacuating staff immediately on the day the fire began.
"The people in 9/11 got sick not because they got burnt, but because of the stuff they were breathing in," said organiser Joe Carolan in a post on the Unite website. "If the company was allowing workers to breathe this stuff in for four hours, they’ve been criminally negligent."
Carolan said Unite members were told to come back to work on Friday, but didn't because they'd already made a deal with the casino they wouldn't have to.
"Corporate is not going back until Tuesday but we're going in today to clean up for you? I don't think so. What are we touching? Have you got Hazmat suits for us? Have you got proper breathing apparatus? What about our pregnant workers, all good for them? Asthmatic workers as well, yes? And if not, how will their income be protected?
"You say it's fine but… The police don't know, civil defence doesn't know when it's safe to go back. So we can't go back on the say-so of SkyCity. We need an independent set of eyes on this. And it shouldn't just be corporate deciding."
SkyCity CEO Graeme Stephens said he breathed in the smoke all of Tuesday, not having a facemask himself.
"It was uncomfortable, but never at a point where I couldn't deal with it. It was a really weird atmosphere in the place. Just empty."
Carolan said this was "not good leadership".
"There should have been enough masks for everyone, including himself. I was beside him at many points during the day. I hope he has not done long-lasting damage to himself."
Carolan said Unite has yet to see SkyCity's air quality reports.
Newshub.
