Cynthia Chaffee’s Manhattan apartment would likely go for more than $5,000 a month if the landlord charged market price. But Chaffee pays thousands less thanks to the city’s long-standing rent stabilization rules—regulations that will expire this year if lawmakers don’t act. The 63-year-old paid $300 a month when she moved into the one-bedroom space in 1978. To Chaffee, the rules governing how much she and more than 2 million other New York City residents pay in rent protect the city’s diversity and character. […] The laws governing the rent paid by Chaffee and more than 2 million other New York...