Thousands of registered nurses will walk off the job Christmas Eve at nine San Francisco Bay Area hospitals, where administrators and a nurses union are locked in a lingering dispute, a union official said Saturday. Nurses and X-ray technicians represented by the California Nurses Association will begin a one-day strike on the morning of Dec. 24 at seven hospitals operated by Sutter Health and at two San Jose hospitals affiliated with the Hospital Corporation of America, said union spokesman Chuck Idelson. Union officials say the strike?the eighth by the association since September 2011?was not called over a salary dispute, but comes as the union and the hospitals remain at odds over staffing levels, health benefits and sick days.