Defense attorneys’ attack against one of the Justice Department’s primary tools to prosecute fraud has begun.

The U.S. Supreme Court heard arguments last week over the merits of the “honest services statute,” which ostensibly requires executives to avoid corrupt activity and execute their duties in good faith. Defense lawyers, however, have long said the 21-year-old law is imprecise in its language, and lets federal prosecutors pursue public and private officials under flimsy pretenses. On Dec. 8 they finally had their big chance in court.