A plainclothes female officer was sexually harassed and abused on Wednesday by a straphanger during rush hour, according to police.

Authorities say suspect Javier Monroy, 39, walked into the 5 train at Grand Central at around 5:50 p.m. as an officer and sergeant with the NYPD's transit anti-crime unit were on patrol on the southbound platform.

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The officers also boarded the crowded train, and as it aheaded toward the Union Square station, police said Monroy approached the plainclothes cop.

Dressed in civilian clothes, the officer reported that the man brushed up against her left hip and then pressed his groin to her body.

The officer immediately said she began to block the inappropriate contact by raising her arm to keep Monroy away.

Once the train pulled up into the station and the officer began to exit the train, she said she noticed Monroy's penis was erect.

That's when the officer called on her team to report she was the victim of a crime. Her partners approached Monroy and identified themselves as police before they cuffed him without any resistance.

The NYPD said Monroy faces forcible touching and sexual abuse charges.