Washington — A majority of U.S. Supreme Court justices appeared skeptical Monday of allowing private “whistle-blowers” to prosecute potentially lucrative suits against state governments in federal court under a Civil War-era anti-fraud law.

The court’s states’ rights-minded conservatives voiced doubts about the legality of such suits, known in legal jargon as qui tam actions. In addition, Justice Stephen Breyer, who typically votes with the liberal bloc on federalism issues, also appeared adamantly opposed to permitting private parties to use the federal False Claims Act to trigger claims against state governments.