A call for response to the office of Seaview Estates, which is also the address for St. Marks Hamilton LLC and Oxford Realty Group LLC, the defendants in the other lawsuit, was not immediately returned.

Advocates for affordable housing and low-income residents have long criticized the city for not aggressively enforcing the law requiring most landlords to accept vouchers. They say the lax enforcement has allowed landlords to flout the requirements and that that has undermined the city’s efforts to reduce homelessness. About 77,000 people are homeless in New York City, according to the most recent estimates available from the federal Department of Housing and Urban Development.

Homelessness began to balloon in 2011 after that state, citing a budget crunch, pulled funding from a rental assistance program called Advantage. The city, under then-Mayor Michael R. Bloomberg, decided the city alone could not fund the program.

Landlords, stuck with renters who could not afford their apartments in 2011, were wary when Mayor Bill de Blasio began introducing a new set of vouchers mostly funded by the city in 2014.

The de Blasio administration has used vouchers and legal assistance for tenants facing eviction as its primary tools to combat homelessness. The administration plans to open 90 shelters over five years to accommodate the homeless. On its worst days, about 60,000 people — about 40 percent of them children — are in the system that uses traditional shelters, hotel rooms and private apartments.

The city wants to stop using hotels and apartments, which are costly and make it more difficult to get services to people so they can move out of the shelter system. But the city has been slow to open the new shelters.

The city offers substantial incentives to brokers and landlords. Brokers can earn a commission equivalent to 15 percent of the annual rent. Landlords can now receive a $3,500 bonus for every apartment rented to a voucher recipient, up from $1,000 offered four years ago. Landlords can also receive a month’s rent to hold an apartment while the city conducts a safety inspection, and the city pays the first year of rent in advance.