PHOENIX (CN) — Arizona unconstitutionally prohibits criminal defense attorneys from talking to crime victims and their families, except through prosecutors, a coalition of attorneys claims in a federal lawsuit against the state.

Arizona Attorneys for Criminal Justice, five criminal defense attorneys and a private investigator sued Gov. Doug Ducey and Attorney General Mark Brnovich on Monday.

They challenge the state’s Crime-Victims’ Rights Implementation Act, of 1991, which implemented the voter-approved Victims’ Bill of Rights, of 1990.

Under the implementing legislation, “The defendant, the defendant’s attorney or an agent of the defendant shall only initiate contact with the victim through the prosecutor’s office. The prosecutor’s office shall promptly inform the victim of the defendant’s request for an interview and shall advise the victim of the victim’s right to refuse the interview,” according to the complaint.

If a victim is killed or incapacitated, the prohibition extends to “anyone within two degrees of consanguinity or affinity to the victim without using the prosecutor’s office as a conduit. And when a victim is a minor child, the defense team may not speak with the child victim or the child’s parents or guardians,” the complaint states.

The coalition of defense attorneys calls the prohibition an unlawful restraint that bars them from engaging in constitutionally protected speech. They say that after talking to a prosecutor’s office, victims are likely to decline to speak to defense attorneys.

In a routine criminal case, the attorneys say, “defense lawyers and members of the defense team should be able to approach crime victims to at least attempt to discuss the facts and circumstances of the alleged crime.”

They say this is crucial in capital cases, where conversations between the defense team and a victim’s family amount to the “highest form of protected speech” and should be suppressed only if the government can show a compelling reason.

“Defense lawyers should not be required to get permission from the government in order to conduct a thorough investigation into their client’s case,” said Amy Kalman, president of the Arizona Attorneys for Criminal Justice. “This law is a textbook example of unconstitutional prior restraint on speech and makes it very difficult for lawyers to meet their obligation to provide effective assistance of counsel to criminal defendants in Arizona,” Kalman said in a statement.

The American Civil Liberties Union of Arizona, representing the coalition, said Arizona is the only state with such a law.

“This law was intended to prevent the harassment and intimidation of victims, but it does much more than that by acting as a complete ban on any speech by criminal defense attorneys to victims,” said Kathy Brody, legal director of the ACLU of Arizona. “Criminal defense attorneys are not interested in harassing or intimidating victims and if they do, they’re already subject to prosecution under Arizona law and professional discipline,” Brody said in a statement.

The coalition says the state could replace the law with a rule “that would address the government interest in protecting crime victims and their families against intimidation, harassment, or abuse, without restricting the speech of plaintiffs and other criminal-defense lawyers and defense teams.”

It seeks declaratory judgment that the law violates the First Amendment, and an injunction against its enforcement.

The Arizona Attorney General’s Office did not respond to a request for comment.