BOSTON — A coalition of booksellers and Internet content providers has filed a federal lawsuit challenging a new Massachusetts law that outlaws the sending of sexually graphic instant messages to minors.

The new law was designed to close a loophole that prompted a court to overturn the conviction of a man accused of sending explicit instant messages to a 13-year-old. The court found that instant messages weren’t covered by the state’s obscenity law. The new law added instant and text messages, e-mail and other electronic communications.

In a lawsuit filed Tuesday, the American Civil Liberties Union and the other groups say the expanded law goes too far, allowing for the censorship of legal discussion, such as contraception and pregnancy, sexual health, literature and art.