The U.S. Supreme Court asked the U.S. House of Representatives, President Donald Trump’s private attorneys and the solicitor general to brief the justices on the “political question” doctrine in relation to cases on subpoenas for the president’s tax documents, suggesting the justices could find they can’t rule on the cases.

In an order Monday, the justices asked the parties and Solicitor General Noel Francisco “to file supplemental letter briefs addressing whether the political question doctrine or related justiciability principles bear on the Court’s adjudication of these cases.”