On October 6, 2010, the California Court of Appeal issued a landmark decision involving Proposition 103 insurance rate approval in MacKay v. Superior Court, B220469 & B223772.

The legal issue, as Division Three of the Second Appellate District explained, was whether the approval of a rating factor by the DOI [Department of Insurance] precludes a civil action against the insurer challenging the use of that rating factor.”

In MacKay, the plaintiff class sued 21st Century Insurance Company asserting that its use of certain rating factors (persistency and accident verification) was illegal and therefore actionable under California’s Unfair Competition Law (UCL”), Bus. & Prof. Code § 17200.

In a unanimous decision, written by Justice Croskey, the Court held "that the statutory provisions for an administrative process . . . are the exclusive means of challenging an approved rate,” precluding a UCL action and therefore ordered the trial court to enter judgment for 21st Century.