Nearly 13,000 healthcare employees at five University of California medical centers plan to strike on Tuesday in a move that threatens to back up emergency rooms and already has forced the postponement of elective surgeries. Vocational nurses, respiratory therapists and radiology technologists say they will walk off their jobs for two days to draw attention to issues they tried unsuccessfully to address at the negotiating table - "chronic understaffing and reckless cost-cutting," said Todd Stenhouse, spokesman for the American Federation of State, County and Municipal Employees.