Mariah Jimenez wore the T-shirt to school on Nov. 3, the day before California voters approved the constitutional amendment prohibiting same-sex marriage.
A teacher ordered the 16-year-old to remove the shirt, but she refused. Principal Michael Ghelber then told her to remove the shirt or remain in his office, so she reluctantly changed shirts and returned to class.
ACLU lawyers Peter Bibring and Lori Rifkin wrote schools superintendent Carole Ferraud that federal and state free-speech laws were violated and the girl deserves an apology.
Ferraud did not return telephone and e-mail messages left Tuesday by The Associated Press.