Randy Garcia thought she might be paying too much for her rent-regulated apartment in Washington Heights in Manhattan: about $1,800 a month. It was more than she could afford with her job handling medical records.

Eventually she asked the state for a history of rent increases on the apartment.

She learned that the landlord, Bronstein Properties, had almost doubled the rent four years earlier, to $1,425 from $761.70. To justify such an increase under the law, Bronstein would have needed to perform more than $30,000 in renovations when the apartment was vacant.

But Bronstein, one of the city’s largest landlords, had not filed a building permit for any work, which would be necessary for most renovations. And Ms. Garcia was dubious that anything had been done.

“For the amount of money I’m paying, I should be living in a palace,” said Ms. Garcia, 49, who lives with her daughter.