The Supreme Court appeared inclined Tuesday to limit federal prosecutors' use of a fraud law that has helped win convictions of high-profile corporate executives and public officials, or throw out the law altogether.

The justices, hearing two challenges to the honest services fraud law, seemed to be in broad agreement that the law is vague and has been used to make a crime out of mistakes, minor transgressions and mere ethical violations.

Justice Stephen Breyer said he worries that the Obama administration's reading of the law makes criminals out of vast numbers of U.S. workers, including possibly employees who read The Daily Racing Form on the job.

"There are 150 million workers in the United States. I think 140 of them would flunk the test," Breyer said.

The vagueness of the honest services statute "is the working problem here," Justice Anthony Kennedy said.

Justice Antonin Scalia called the law "a mush of language" and pointed out that federal prosecutors have used it different ways in different prosecutions. If the Justice Department can't figure out what is embraced by this law, "I don't know how you expect the average citizen to," Scalia said.