A top de Blasio official has been calling developers of affordable rental buildings about a new regulation that would require them to house homeless families—the administration’s latest attempt to stem the city’s record-setting shelter population.

Vicki Been, commissioner of the Department of Housing Preservation and Development, recently made the calls to a handful of developers who received a now-defunct tax exemption called 421-a, according to sources with knowledge of the calls. The tax exemption requires that at least a quarter of a building’s units be enrolled in the city’s affordable housing program.