This spring, a tenant called the Metropolitan Council on Housing’s hotline to ask if his landlord could legally take away the rent discounts he’d been getting for years. Recognizing a jump in the neighborhood’s housing market, his building’s owner wanted to significantly raise the rent, to the maximum level allowed under the state’s rent regulation laws.

Don’t worry, Met Council organizer Dave Powell told the caller, New York’s housing laws prohibit landlords from making a switch like that until the current tenant moves out. Powell’s answer was correct–until the next day, May 22, when the Appellate Division of the Manhattan Supreme Court ruled that anytime a lease comes up for renewal, landlords can raise the rent to the full amount allowed under state rent regulation.

For tenants in neighborhoods like Harlem, Bushwick and Williamsburg, where once-struggling housing markets are heating up, rents could as much as double. And some advocates predict it could mean a spike in evictions. “This will give landlords a real incentive to jack up rents if they have other tenants who are willing to pay that price,” says Powell.

The appellate division’s 3-2 ruling threw out a decision made by the state Division of Housing and Community Renewal in 1997 that rejected a landlord’s request to charge higher rents for tenants who had been paying what are technically known as “preferential” rents. In that case, the Missionary Sisters of the Sacred Heart sought to raise an East Village tenant’s rent by $70, 5 percent more than the rate they’d charged for the previous two years. The court said there is no reason to conclude “that the preference was to survive after the economically depressed market recovered.”

Landlords applaud the decision, saying the reductions were always meant to be short-term. “It’s always offended me that if an owner did a favor for a tenant, that became permanent,” says Dan Margulies, president of the Community Housing Improvement Project, a landlord group.

Meanwhile, tenants hope DHCR appeals. “I’m really scared they’ll decide to not fight this,” says Ken Rosenfeld, legal director for the Northern Manhattan Improvement Corporation. “If it stands, it’s a major blow for tenants in gentrifying neighborhoods.”