Although they are temporary and last just as long as the application period, the retroactive increases can raise a rent bill 20 percent or more for a few years.

Under state law, the tenants may pay off the retroactive increases a month at a time, rather than repaying the entire amount owed immediately.

Until then, they are paid under the old formula, with no provision for retroactive increases.

It also prohibits retroactive increases of criminal punishments.

The increases, retroactive to July 1, would be reflected in bills sent out in January.

Under the court ruling won by the landlords, the tenant would be required to pay the retroactive increase - $1,336.50 - over a period of 21 months.

For tenants who have rented a vacant apartment after the rehabilitation occurred but before the allowance was granted, retroactive increases seem especially puzzling and unfair.

Auto companies, for example, gave profit-sharing bonuses to their workers, and the Social Security Administration paid retroactive increases in benefits.

Both proposals also included some retroactive increases.

But the process takes so long, owners say, that many tenants will have moved before retroactive increases can be collected.