Man rubs crotch on woman on train before discovering she is a plainclothes police officer

Man charged with forcible touching and sex abuse

Felipe Mondragon was taken off the uptown number 6 train in handcuffs at 23rd Street Station (AFP)

A man has been arrested after rubbing his crotch against a woman on the New York subway who was actually a plainclothes police officer.

Felipe Mondragon, 52, rubbed against the NYPD detective's thigh as the uptown 6 train left Union Square station, the New York Daily News reported.

The detective, who has not been named, was travelling with her partner and a sergeant as part of a plainclothes operation.

The trio arrested Mondragon and he was taken off the train in handcuffs at 23rd Street Station.

He was charged with forcible touching and sex abuse.

Mondragon, of Jackson Heights, has two prior arrests on his record but both are sealed.

It comes after a similar arrest was made at the East 59th Street station after Osa Ayanru, 38, ground his crotch against another undercover police officer's leg.

The officer was part of the NYPD Transit Bureau's Anti-Crime Squad, which patrols the subway looking for crime.