The government announced on Friday that Ontario's emergency brake will be activated for some regions.
Both Thunder Bay District and Simcoe-Muskoka District Health Units will move into grey-level lockdown.
The move, which is being made to curb a recent spike in transmissions and community spread of COVID-19, is scheduled to come into effect on March 1 at 12:01 a.m.
"The recent modelling shows us that we must be nimble and put in place additional measures to protect Ontarians and stop the spread of COVID-19," Christine Elliott, deputy premier and minister of health, said.
The government also announced that other regions are also seeing a shift when it comes to their coloured zones.
Niagara Region Public Health, which was originally in the grey zone, will now be moved to the red.
While Chatham-Kent Public Health, Middlesex-London Health Unit and Southwestern Public Health will be moved to the orange zone.
Haldimand-Norfolk Health Unit and Huron Perth Public Health will move up to the yellow zone.
And Grey Bruce Health Unit will now see itself in the green zone.
Peel Public Health, Toronto Public Health and North Bay Parry Sound District will continue to be under Ontario's stay-at-home orders until at least March 8.