A class action suit reportedly filed against Zenith National Insurance Corp, was without merit and the company said it intends to defend the litigation vigorously. The complaint filed by Back Doctors Chiropractic in the United States District Court for the Central District of California alleges that Zenith improperly discounted medical bills submitted for payment. Zenith has not yet been served a copy of the complaint. Zenith is a specialty workers’ compensation insurer based in Woodland Hills.