A subway conductor was sexually assaulted by her supervisor on a moving train, she claims in a lawsuit.

Faith Sanders says her boss, Lloyd Senior, jumped aboard the Q train in Coney Island on Nov. 6, called her pants “too tight” and started asking about her bra size, according to Brooklyn federal court papers.

Senior pinned her against the wall, opened her shirt and groped her breasts, the suit says.

Sanders went to cops, who charged Senior with sexual abuse. But the Brooklyn District Attorney’s Office declined to prosecute.

The MTA said it could not substantiate the accusation, so Senior was returned to service, but given a different position.