Image courtesy of Gensler

Developers have submitted their formal proposal to Boston city planners for the partial conversion of a Back Bay hotel into student housing, a project that’s generated opposition from local elected officials and a hospitality union.

The 428-room permanent conversion of the Sheraton Boston’s south tower at 39 Dalton St. would accommodate 856 Northeastern University students.

The owners of the property, Hawkins Way Capital and Varde Capital, bought both Sheraton towers in 2022 for $233 million and announced plans to repurpose the newer of the two towers, completed in 1975.

The proposed project includes updates to the tower’s 6,000 square feet of vacant ground-floor retail space, and creation of an 18,000-square-foot amenity level on the third floor, according to a project notification form submitted to the Boston Planning & Development Agency.

Updates include a new main entrance for students and new plantings, shade trees and seating at the outdoor plaza.

Boston city councilors approved a resolution asking the owners to reconsider the dorm conversion in 2022, following protests by hospitality workers’ union Unite Here Local 26, representing 100 hotel workers.

Northeastern started renting the south tower in 2018 as overflow housing. Since 2019, the university has been seeking approval for a 25-story development at 840 Columbus Ave., and pent-up demand for enrollment in the wake of COVID led to a 17 percent increase in 2021-2022 applications. The university received nearly 91,000 applications for 2,519 slots for the class of 2016, officials said at a BPDA-sponsored presentation last December.

Nearly two-thirds of Northeastern’s 16,000 students in Boston live in university managed or affiliated housing, according to documents submitted to the BPDA in December.

The Sheraton project requires either a conditional use permit from the Zoning Board of Appeal or approval of a planned development area amendment, developers said in the project notification form. The project team includes Gensler and Ray Dunetz Landscape Architecture.