But Alicia Glen, the deputy mayor for housing and economic development, said that separate front doors were not in keeping with the administration’s principles of equality, and that the city was working to change the rules to prohibit them.

“Walking into a building should not be any different based on income status,” Ms. Glen said in an interview.

From the street, the luxury condominium tower in the middle of the debate, at 40 Riverside Boulevard, and its six-floor affordable segment seem to blend seamlessly and appear as one structure. But the lower-income renters, who will pay $850 a month for one-bedroom apartments and $1,100 for two bedrooms, according to the developer, will go through a door facing 62nd Street while the condo owners will come in through a door facing the Hudson.

New York and other cities use a variety of tax breaks, subsidies and additional incentives to encourage developers to build affordable housing. In the case of 40 Riverside, the developer, Extell Development Company, is using a program called inclusionary housing, which allows it to build more square feet than the zoning code would otherwise allow in exchange for a certain number of lower-rent apartments. Those additional square feet can be used at 40 Riverside, but Extell plans to transfer them to another project, which the law allows.

The affordable units do not have to be in the same location, as long as they are within the same community district or, if in another district, no farther than half a mile away.

Image Mayor Bill de Blasio, who remains focused on reducing income inequality, is seeking the construction of 80,000 new affordable units over the next 10 years. Credit... Bryan Thomas for The New York Times

Gary Barnett, who is Extell’s founder and president, said that having the affordable apartments incorporated into the condominium tower would have meant “giving away” the most valuable units.