A straphanger swipes their MetroCard at the Utica station in Brooklyn. (Photo by Lauren A. Smith/amNY)

Small-time criminals illegally selling MetroCard swipes and jamming vending machines are on the loose, and union officials and transit advocates predict the scourge will get worse when the MTA lays off personnel overseeing the stations.

“New York is not a place you can go on the honor system. This isn’t Canada,” said Maurice Jenkins, union vice president for stations.

Since the MetroCard debuted in 1994, crooks have illegally sold swipes to straphangers by using unlimited cards or bending them in a way to provide free rides. The MTA installed anti-tampering software in its turnstiles to stymie the swindlers, but the NYPD still arrests about 20 people a month for selling swipes from the doctored cards, according to agency figures.  About another 80 are caught hawking rides from un-doctored cards.

“It’s a safety issue,” said Carol Labozzetta, 42, an Astoria rider. “What else could they be doing illegally?”

Two hot spots for the crooks, also known as “trolls,” are the 111th Street station on the No. 7 and the 49th Street stop on the N, where they targeted unsuspecting tourists, union officials and workers said. Those caught selling or buying the swipes are fined $100.

But the crooks inconvenience all riders, as they often jam the bill dispensers in  MetroCard machines with a toothpick or a straw to force straphangers to buy from them instead. A machine at the 66th Street station on the No. 1, for example, was recently jammed for days, union officials said.

“They coerce people to buying swipes. It worries my greatly,” said Gene Russianoff, of the Straphangers Campaign.

Arrests for selling swipes have fallen in recent years, with police nabbing 1,200 offenders last year, an NYPD spokeswoman said. But advocates predict the crime could grow in May when the MTA eliminates 600 station agents, who call police when they see people selling swipes.

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“We will, as we always do, consult and work with (police) to combat” the illegal swiping, NYC Transit spokesman Paul Fleuranges said.

At the Utica Avenue station on the No. 4, a man was recently seen selling swipes for the discounted price of $1.50. When he was questioned by a reporter, he said it was “so that (he) could get something to eat.”

Nicholas Klopsis contributed to this story.