NEW YORK (AP) — Inspired by his own experience living in a New York City apartment building that was converted into high-priced condos, a 71-year-old former state regulator is taking on developers citywide on behalf of seniors and disabled tenants.

Walter Goldsmith claims in a state lawsuit filed late Tuesday that landlords have ignored a decades-old law that requires them to give tenants 62 and older and those with disabilities the option to stay-on as renters in their apartments rather than move away or buy themselves.

Experts say the case could provide an extra layer of protection to vulnerable market-rate tenants who have lost housing security as rent-stabilized and regulated apartments have decreased in recent years.

"It's fair to say these people are entitled to some stability and harmony in their lives," said Goldsmith, who for the past 10 years has lived in a cozy one-bedroom in a 31-story building on Manhattan's Upper East Side.

Landlords had previously argued, as Related Companies did to Goldsmith in correspondence provided to The Associated Press, that the option for seniors and disabled renters to stay-on only applied in cases where buildings were converted via eviction plans — that is, when 51 percent of the building's units were purchased by people who live there.

But in so-called non-eviction plans, where only 15 percent of the apartments have to be sold for the plan to become effective, tenants are often pushed out because their leases aren't renewed or they're given hold-over leases during the conversion process, real-estate lawyers said.

"A lot of buildings have tenants who are not protected under rent stabilization and rent control, particularly in Manhattan," said longtime real estate lawyer Kevin McConnell, who is not part of the lawsuit. "What we have been seeing is, where once tenants were all protected and had very few vacancies, now you walk in and there are vacancies all over the place."

The attorney general's real estate finance bureau regulates the conversion process and has in recent years stepped up its enforcement and regulation of conversions. On Nov. 10, the office issued new emergency regulations that require building owners to provide seniors and disabled tenants explicit notice of their right to choose to continue renting at rates that won't soar. A spokesman for the office declined to comment.

The lawsuit, which claims $100 million in damages, seeks class-action status. A spokeswoman for Related Companies, the parent company of Carnegie Park Tower, LLC, which owns Goldsmith's nearly 300-unit, $483 million apartment building, said in a statement that while officials hadn't seen the court papers, the company "scrupulously followed the statute and adhered to every applicable regulation."

Marc Held, the attorney bringing the lawsuit with Goldsmith, said at least a quarter of the building's renters are either elderly or disabled, including at least one blind tenant.

"These are apartments that are triple in value vacant what they are with a rent-regulated tenant in there," he said. "There's a tremendous financial incentive not to comply with the law."