In an hour-long argument in Washington Monday, a majority of the justices voiced doubts about a 1992 federal law that bars wagering on individual sporting events in every state except Nevada. New Jersey, which is attempting to repeal its prohibition on sports gambling, contends the federal law violates states' rights.

Justice Anthony Kennedy, often the court's swing vote, said the federal law "leaves in place a state law that the state does not want."

Should the high court strike down the federal law, other states could move quickly to take part of the $150 billion the casino-backed American Gaming Association says is wagered illegally every year. By some estimates, more than a dozen states could have legal sports gambling by the end of next year.

New Jersey Governor Chris Christie, who sat in the front row for the argument, told reporters afterward that his state is ready to begin sports betting within two weeks if it prevails. The court will rule by June.