In Parks v. MBNA America Bank, N.A., ___ Cal.4th ___ (Jun. 21, 2012), the Supreme Court held that the National Bank Act preempted a UCL "unlawful" prong claim predicated on violation of Civil Code section 1748.9, "a California law requiring that certain disclosures accompany preprinted checks that a credit card issuer provides to its cardholders for use as credit." Slip op. at 1.
The opinion says nothing substantive about the UCL in particular; its focus is on section 1748.9 and the provisions of the National Bank Act.