Three eighth-grade girls from Griffith Middle School in Hammond, Indiana, were expelled after joking about the classmates that they would like to kill on Facebook, which was seen by a classmate's mom who told on the girls.
The 14-year-old girls were expelled in January by school officials who told the students that they had violated school policy against bullying.
ACLU attorney Gavin Rose filed a lawsuit, claiming that Griffith Public Schools has violated the girls' First Amendment rights.
The lawsuit says that the Facebook posts were made after school on the girls' personal electronic gadgets.
Rose claims the girls were clearly joking because their posts included smiley faces, emoticons and "LOL," which stands for "laugh out loud" in Internet language.
Rose told the Associated Press: "The fact of the matter is that no reasonable person looking at this conversation would think that these girls were going to go out and inflict harm on anyone. If you make a legitimate threat against someone ... you don't follow it up with an emoticon. Schools do not possess infinite reach into the private lives of their students."