Minneapolis ? More than 12,000 nurses walked off the job Thursday for a one-day strike at 14 Minnesota hospitals, a show of force being watched by many across the country as a test of how fiercely a new national nurses’ union can flex its muscle.

Nurses say they are being asked to care for too many patients at a time, and strict ratios are necessary to protect patient safety. The hospitals, all in the Minneapolis area, counter that patients are safe and that the walkout is a headline-grabbing stunt to build membership and clout for the fledgling union.

About the same number of nurses had wanted a simultaneous strike in California over the same issues, but were blocked temporarily earlier this week by a San Francisco judge.

Labor experts say unlike other unions that might shy away from striking during a recession, nurses have certain job security because they are in demand and can’t be outsourced.