The U.S. Supreme Court heard arguments Monday over Texas’ hotly debated abortion ban, and although it could be days or weeks before the court issues a ruling, justices who will cast key votes on the issue signaled apprehension over the law’s wider implications.

Conservative justices Brett Kavanaugh and Amy Coney Barrett, who both tend to favor abortion restrictions, hinted at some skepticism over the Texas law while hearing from abortion providers and the U.S. Justice Department. The arguments did not concern the legality of a six-week abortion ban but rather the unique structure of the law and whether its opponents can mount federal court challenges against it.

The legislation deputizes citizens, not the state, to enforce the ban and offers a $10,000 bounty to anyone who successfully sues someone for “aiding or abetting” patients seeking abortions in Texas. It’s that unusual design, one that has little historical precedent, that has made it so difficult to wage legal battles in federal court.