An organization that fiercely defends the rights of Jewish women is being sued by a former mail-room clerk for allegedly violating his religious beliefs — and firing him after he complained.

Marshall Garvin, 65, an observant Jew, claims his boss at Na’Amat USA Inc., of Manhattan, refused to let him use his lunch hour to leave work early to recite Kaddish — a memorial prayer for his mom.

His boss “was cursing me and using foul language, saying ‘Don’t BS me by leaving early,’ ” Garvin claimed.

His lawsuit, filed in Bronx Civil Court Monday, charges that he was axed in May 2011 when he complained about his treatment. His boss said Garvin was one of three workers laid off in a downsizing.