As huge swaths of the city get rezoned for development, a growing group of tenants, housing advocates and city officials want to put affordable housing on the map.

Gathered Wednesday on the steps of City Hall, the group unveiled a new report that argues in favor of mandatory “inclusionary zoning”: requiring developers who build in newly rezoned areas to make a certain percentage of their units affordable.

While the amount and the level of affordability will likely vary by neighborhood, the goals are clear: protect renters, encourage urban infill and maintain economic diversity. “When the city does these major rezonings, it’s creating enormous wealth for developers,” said Assemblymember Dick Gottfried. “It’s only fair for them to give something back.”

The report, produced by PolicyLink, a national research organization, and Pratt Institute Center for Community and Environmental Development, a planning advocacy group, estimates that 15,000 permanently affordable units could be created if New York applied inclusionary zoning to the more than two dozen areas currently being rezoned. The report points out that many other U.S. cities—including San Francisco, Denver and Boston—have already implemented similar rules.

PICCED’s Brad Lander, who co-authored the report, cites several studies showing that inclusionary zoning adds affordable housing without hurting the industry overall. “All the evidence from around the country says mandatory works,” he said. “It is viable to do this.”

Some private developers disagree, arguing that the way to get more affordable housing is to loosen regulations, not add more. “We believe the city of New York has no legal authority to impose mandatory low-income housing,” said Steven Spinola, president of the Real Estate Board of New York, adding that his members would probably sue the city if the zoning comes to pass.

Thus far, the Bloomberg administration has only endorsed voluntary incentives. At a recent meeting of Brooklyn’s Community Board 1, for example, planning commissioner Amanda Burden and housing commissioner Shaun Donovan unveiled an “Inclusionary Bonus Plan” for Greenpoint-Williamsburg that would increase the allowable density for developers who agreed to make 10 to 15 percent of their apartments affordable.

Councilmember David Yassky, who represents the district, says it’s a major improvement over past proposals—though he’s still pushing for mandates instead. “I think the amount of popular support is so great, the administration understood that it needed to address the issue of affordability,” he said. “At least now we’re making progress.”