For some of the more than 100,000 travelers who use the Port Authority Bus Terminal each day, a second-floor men’s room is their first or last stop in New York City. The facilities are what you might expect: toilets, urinals, hand dryers.

But above the row of sinks, a posted sign offers an atypical note of caution: “Restrooms are patrolled by plain clothes officers.”

It is not an idle warning.

Port Authority police officers have arrested more than 60 people this year in the bus terminal on public lewdness charges, a sevenfold increase over the same period last year. Most of those arrested were accused of masturbating in the second-floor bathroom. According to court records, they were observed by plainclothes officers, who were often standing next to them at an adjacent urinal.

At least a dozen of those arrested are represented by the Legal Aid Society, whose lawyers say their clients — some of whom say they were merely urinating — were victims of aggressive and intrusive police tactics.