New Jersey argues that the federal law infringes upon state sovereignty as laid out in the U.S. Constitution.
Trump, who takes office on Friday, is no stranger to gambling in New Jersey. He once owned casinos in Atlantic City but left after his businesses filed a series of bankruptcies.
New Jersye Governor Chris Christie served as an advisor to fellow Republican Trump during the New York real estate developer's presidential campaign but was removed as the head of Trump's transition team after the election.
Trump has not yet nominated anyone to fill the role of solicitor general, the Justice Department lawyer who represents the federal government before the Supreme Court. It is the solicitor general who would officially file the brief laying out the new administration's position in the gambling case.