At two million acres, the Greenbelt forms a ring of land north of the city where development is restricted. The intention was to protect areas such as the Niagara Escarpment and the Oak Ridges Moraine from rampant development.
Susan Swail of Environmental Defence told CBC's Mike Wise that no sections of the Greenbelt should be lost to development.
"There's generations of land already allocated for development, there's no reason to go out into the Greenbelt. If we grow smarter, grow up and not out, there's no reason we can't have a protected Greenbelt."
Bradley Harman is a real estate council president in Brampton, an area under extreme growth pressure.
"Brampton obviously has been a very fast-growing market," he said. "The Greenbelt has contributed again to kind of holding the market into one specific location. It provides a boundary for which urban sprawl is limited.
"I'd say we're approaching the brink of where we can develop. We're right along the borders of Brampton, encroaching onto Caledon at the moment. I don't imagine there's much more space to grow out at this point."
Harman says the Greenbelt is too valuable a resource to destroy. He wants towns and cities to adopt stronger smart-growth strategies to better use the land we can build on.
"There's going to be some serious conversations as to what and where we can build," he said. "Developers will constantly be looking for the easier ways to build and the easiest way to build is on fresh farmland."
Concerns over new highway plans
The need for new homes isn't the only factor putting pressure on the Greenbelt.
The province is studying routes for the GTA West highway, which would cut across the north end of Brampton and Vaughan to connect Highway 401 with Highway 400.
Swail says the highway plan runs contrary to the ideals of the Greenbelt and would take about 2,000 acres of prime farmland out of production.
"It's a really bad idea and I think it should be stopped, and I think it will be stopped," she said.
The Ontario government is currently holding public consultations about the Greenbelt.