The U.S. Supreme Court declined to review a lower-court decision saying that salary history is not a "legitimate factor other than sex" that justifies a pay differential, and therefore that use of salary history violates the federal Equal Pay Act.

In Yovino v. Rizo, the U.S. Court of Appeals for the Ninth Circuit ruled in 2018 that the use of salary history violated the EPA. Then, in a bizarre twist, the Supreme Court vacated that decision because the Ninth Circuit judge who wrote the opinion died before the opinion was issued, and there were not enough remaining judges agreeing with him to create a majority.

After the case was sent back to the Ninth Circuit, that court essentially affirmed the 2018 ruling. The employer then petitioned the Supreme Court for certiorari.

Thursday the Supreme Court denied the employer's petition, which means the Ninth Circuit decision will remain in place. Although the decision applies only in the Ninth Circuit states of Alaska, Arizona, California, Hawaii, Idaho, Montana, Nevada, Oregon, and Washington (and Guam and the Northern Mariana Islands), employers everywhere are urged to be cautious when using salary history as a factor in determining pay. In addition to concerns under the federal Equal Pay Act, many states have enacted legislation saying that use of salary history violates their state equal pay laws.