One of the most controversial—and costly—rules in U.S. Securities and Exchange Commission history faced tough scrutiny Tuesday by panel of federal appellate judges, who questioned whether the requirement that publicly traded companies disclose the use of certain minerals from the war-torn Democratic Republic of the Congo violates the First Amendment.

“Is the objective to stigmatize companies?” Senior Judge A. Raymond Randolph of the U.S. Court of Appeals for the D.C. Circuit said during oral arguments before a packed courtroom in Washington. Randolph described the disclosure requirement as “a slippery slope.”