California’s Supreme Court on Thursday made it tougher for employers to dispose of whistleblower retaliation claims, finding that a state law, and not a federal test, is the proper standard for courts to use in deciding whether a worker was improperly fired or denied promotions.

The unanimous opinion in Lawson v. PPG Architectural Finishes was written by Associate Justice Leondra Kruger, now a potential frontrunner for a seat on the U.S. Supreme Court. The opinion is her first since U.S. Supreme Court Justice Stephen Breyer announced that he will retire at the end of the current term, placing her and her writing under a microscope.