The three say allowing a private developer to build a 66-room hotel and 15 tent cabins at Maligne Lake in Jasper National Park would violate Parks Canada policy.
They say the hotel would open the doors to similar projects that would degrade the wilderness experience of national parks across the country.
Their objections are in an open letter released as Jasper National Park staff grow closer to making a decision on the proposal from Maligne Tours.
The tour company says it's necessary to upgrade and modernize its lake facilities.
It says the new hotel wouldn't require any new land to be developed.