The New York Court of Appeals on Tuesday, Jan. 7, held a hearing on five cases that involved claims that tenants were overcharged rent by their landlords, who had removed their apartments from rent stabilization while collecting J-51 tax benefits.

Each of the cases cite the pivotal 2009 Court of Appeals ruling, Roberts v. Tishman Speyer Properties, in which the high court ruled that landlords couldn’t receive J-51 tax benefits in New York City if they removed an apartment from rent stabilization via luxury decontrol.

At issue in these cases is the application of the lookback period, the window of time the state can assess treble damages for rent overcharges. This lookback period was recently extended to six years from four by the passage of the Housing Stability and Tenant Protection Act, the largest overhaul of the state’s rent laws in decades.

The Court of Appeals will decide whether that extension also applies to ongoing overcharge cases, which would substantially increase the landlord’s liability. If the new law should be interpreted as retroactive, this would mean actions pending a final determination or on appeal would be subject to the new law. And this would allow a lookback of more than four years to find what the tenant’s rent should have been if the unit hadn’t been deregulated.