A legal challenge to the Securities and Exchange Commission’s Conflict Mineral Rule, which will require companies to disclose the use of certain metals throughout its supply chain, is heating up, and it could succeed in changing the final version of the rules.

A federal appeals court heard oral arguments from plaintiffs challenging the rule, including the National Association of Manufacturers, U.S. Chamber of Commerce, and the Business Roundtable, earlier this month, and the SEC’s defense of it. Tough questioning directed toward the SEC by a three-judge panel led some legal experts to predict the court could deem the rule unconstitutional.