The call by the group known as the Elliot Lake Mall Action Committee follows testimony at a judicial inquiry into the tragedy by a senior Labour Ministry bureaucrat, who said her officials had acted properly.
"Everyone has been thoroughly investigated by the Ministry of Labour, except the ministry itself," said John Pomerleau, chairman of the group. "It's not right."
In her testimony last week, Sophie Dennis, an assistant deputy minister, said the ministry bore no responsibility for the tragedy in which Lucie Aylwin, 37, and Doloris Perizzolo, 74, died and dozens were hurt.
"The employer is responsible for the protection of their workers; supervisors are also responsible; and workers are also responsible," Dennis testified.
Ministry officials, Dennis said, were only a "check on the system" and none of her officials had been charged or disciplined as a result of the disaster.
Doug Elliott, who represents the action committee, called Dennis's position unacceptable.
"What on earth does she think Lucie Aylwin could have done to protect herself from that roof caving in on her?" Elliott said in an interview.
"What we're dealing with here is a whitewash of the Ministry of Labour's activities that is directed by Ms. Dennis herself."
The group wants Ontario Labour Minister Yasir Naqvi to call in federal occupational health and safety inspectors to investigate the ministry's role and recommend whether charges or other action might be warranted.
The inquiry has heard how a Ministry of Labour inspection office was housed in the Algo Centre Mall for 10 years from 1985 until 1995, but did little to address conditions in the leaking mall.
In fact, Dennis didn't know the mall office existed.
The ministry received more than 30 complaints of health and safety violations before the collapse on June 23, 2012, but never issued a single order to fix the leaky roof that prompted residents to dub the mall the "Algo Falls."
An employee complaint on the day of the collapse resulted in an emailed response pointing at a toll-free number to request an inspector.
"The inaction of the Ministry of Labour stands in stark contrast to the drastic action they took after the collapse," Elliott said.
Among other things, the ministry thoroughly investigated after the tragedy, and to date has charged an engineer under occupational health and safety rules.
Pomerleau said Dennis was in a clear conflict of interest in her "cursory" investigation of her own officials which was based only on a review of reports filed by ministry inspectors.
At the legislature, Naqvi said he saw no need for a probe given the ongoing judicial inquiry, which is also looking into government processes.
"Let's let the inquiry do its work and what recommendations come out of it," Naqvi said.
"It would be fairly speculative to start talking about what should be done."
The judicial inquiry, which began hearing evidence in March, has no power to recommend charges or discipline against anyone.
Commission officials had no comment on the call for an investigation.