On the heels of a class-action lawsuit that accuses the NYPD of making unjustified arrests, Police Commissioner Raymond Kelly issued new rules for how cops can patrol in privately owned apartment buildings, the Daily News has learned.

The order, issued Monday, says officers need probable cause to arrest someone for trespassing — and that police should take “reasonable measures,” such as asking for ID or building keys, to verify whether someone who is stopped and questioned has a right to be there.

In the past, police have also taken the additional step of verifying those claims — by knocking on someone’s door, for example. But that scenario isn’t addressed in the new order.

Landlords who register for Operation Clean Halls give police permission to routinely “vertically patrol” their buildings.

But the New York Civil Liberties Union filed a federal suit in March that accused the NYPD of routinely violating the rights of residents — most of them black or Latino — by making unjustified trespassing arrests in those buildings.

The group said residents have learned to carry ID at all times or risk getting arrested while throwing out their garbage or getting their mail.

It also said police assumed the program gave them the right to stop people outside the buildings participating on Clean Halls.

“It absolutely seems like the rules were not spelled out clearly at all,’’ said Alexis Karteron, senior staff lawyer for the NYCLU. “It seems like the order recognizes there are serious problems with the program, but the NYPD still as a long way to go.”

Kelly has said Operation Clean Halls is intended to add a layer of security for people who can’t afford to live in dorman buildings.

(Source: NY Daily News)