The managers argue the development would violate Parks Canada's own policy and endanger local species at risk, including the woodland caribou.
The proposal would see construction of a 66-suite hotel and 15 tent cabins on the north side of Maligne Lake.
There is already a public boat launch at the site. A commercial operator who offers boat rentals and tours at the site wants to build the overnight accommodations.
Kevin Van Tighem, one of the managers, says he has several concerns, among them that the development would close the space off to the public.
"Why would we privatize one of the most beautiful public destinations in the park?" he said in an interview with CBC News.
The authors of the letter to Environment Minister Leona Aglukkaq also argue that any commercial development at Maligne Lake violates Parks Canada's own policy.
"Currently, only day use is allowed at Maligne Lake. Maligne Tours' proposed resort contravenes Parks Canada's 2007 policy that prohibits any new commercial accommodations outside park town sites, and places clear negotiated limits on all existing outlying commercial accommodations," the letter states.
Changing the rules?
Van Tighem is also worried what approval of the development might mean for future proposals.
"It basically says to anybody else who has had a 'no' in the past, well we can talk about 'yes' now, because we just changed all the rules," he told CBC News.
Two years ago, there was a similar controversy over a proposed Glacier Discovery Walk, a viewing platform extending over the Sunwapta Valley at the end of a 400-metre trail along Jasper's Icefields Parkway.
The tourist attraction was eventually approved by then environment minister Peter Kent and it opens officially next month.
Eric Hebert-Daly, executive director at The Canadian Parks and Wilderness Society, voiced his concern over that development and its impact on the local ecosystem.
He has similar concerns for Maligne Lake, arguing any development could further endanger the local caribou herd, which has already been reduced from 30 to just five animals.
"We obviously want to encourage people to go out and get into nature and to have that experience, but it can not come at the cost of nature itself," Hebert-Daly said.
Parks Canada is considering the proposed development. Hebert-Daly said he expects a decision soon.