Another Financial District office building might be turned into apartments.

Mahoney Development filed a proposal to convert a 10-story, 193K SF office building at 50 Congress St. into 171 apartment units. The project would be the second-largest office-to-residential conversion in Boston, behind Synergy's Washington Street project.

The proposal, filed Monday, sets aside 20% of the units as affordable and includes roughly 6,700 SF of ground-floor retail. A joint venture between Jumbo Capital Management and Guggenheim Real Estate last acquired the property in 2017 for $79M.

There are 22 conversion projects totaling roughly 1,500 units proposed throughout the city. The majority are in the city's central business district.

At the time of its acquisition in 2017, the building was 90% occupied by 60 tenants, including Turco Legal, Arena Care & Wellness and burrito restaurant Boloco.

It has been a big month for office conversions. Synergy filed plans two weeks ago for a 250-unit conversion of the 11-story 294 Washington St. office building. That would become the largest conversion in the city.

The projects come after Mayor Michelle Wu decided to extend the office-to-residential conversion program at the end of last year. The program began in 2023, offering developers an average tax reduction of up to 75% of the standard tax rate for up to 29 years.

CORRECTION, FEB. 3, 12:10 P.M. ET: A previous version of this story included incorrect square footage for the proposed ground-floor retail portion of the project. The story has been updated.