DES MOINES, Iowa (AP) — The parents of a 14-year-old Iowa girl are suing a county prosecutor to try to stop him from filing criminal charges against the teen after she sent suggestive photos of herself to a boy.

Marion County Attorney Ed Bull has threatened to charge the Knoxville girl with sexual exploitation of a minor or child pornography. Bull has said she can avoid the charge if she signs an admission of guilt, performs community service and temporarily gives up her laptop and cellphone.

The lawsuit was filed in September and amended Thursday to add new arguments and to add the American Civil Liberties Union of Iowa as attorneys for the girl. The ACLU says it’s seeking to protect the girl’s rights to free speech and freedom of expression. The ACLU says the photos don’t show nudity and are not obscene.

Bull has asked the federal court not to intervene in a state prosecution.