The province has documented almost 15,000 new cases of COVID-19 over the past five days, and hospitals now have more COVID-19 patients in intensive care than at any other time during the pandemic.
"The spread of COVID-19 has never been greater in Toronto, with variants of concern increasing both the risk of transmission and the risk of serious illness or death", the statement said.
A spokeswoman for Health Minister Christine Elliott said the shutdown was aimed at dealing with the third wave of the pandemic, but noted it takes time for the intended effects of the measures to be realized due to the incubation period of the virus.
The letter asks Williams to issue a province-wide stay-at-home order, close non-essential businesses (and be stricter about which businesses quality as "essential"), mandate staffing limits where possible, set strict capacity limits in open businesses, restrict people from travelling within Ontario, offer paid sick days to essential workers and move schools online in hard-hit areas.
The letter was signed by Toronto's Medical Officer of Health Dr. Eileen de Villa, Peel Region's Medical Officer of Health Dr. Lawrence Loh and Ottawa's Medical Officer of Health Dr.
Others were quick to react as well. "And again, we have to focus on where we see the problem three regions, York, Peel, in Toronto represents 60 per cent of the COVID cases".
He said the government will be "very clear tomorrow".
The decision comes a day after neighbouring Peel Region opted to shut down its schools on Monday.
"Our government will continue act on the advice of the Chief Medical Officer of Health who will review the science, data and trends along with collaborating with local medical officers of health and our team of expert health officials on if and when public health measure can be loosened or strengthened".
Ford had tightened restrictions across Ontario last week.
"Collectively, we have failed our children".
You can read the full letter via the tweet below. Schools will be closed for at least two weeks, starting Tuesday, although the second week is the scheduled April break for staff and students.
Ontario also reports 494 patients in intensive care because of COVID-19 and 293 on a ventilator.