DOVER, Del. -- The American Civil Liberties Union has filed a federal lawsuit on behalf of a group of young women who claim their constitutional rights were violated when they were ordered to leave a book-signing featuring Sen. Rick Santorum, R-Pa.

The lawsuit, filed Tuesday in U.S. District Court in Wilmington, claims that two of the women were arrested for trespassing last year and three others threatened with arrest because of their political views.

According to the lawsuit, the women went to a Barnes & Noble store at Concord Mall in Wilmington to challenge Mr. Santorum at an event advertised as a book-signing and discussion of his book, "It Takes a Family."

The women were ordered to leave by a uniformed state trooper providing security at the event after a member of Mr. Santorum's promotional team overheard them talking before the Republican lawmaker arrived, according to the lawsuit.

"The advertisements said 'book signing and discussion,' not 'discussion only if you agree with the senator,' " said Julia Graff, staff attorney for the Delaware chapter of the ACLU, which joined with the Pennsylvania ACLU chapter in filing the lawsuit. "The trooper denied these women their right to share their views with an elected official. This is precisely the kind of conduct the First Amendment was designed to guard against."