More than 20,000 registered nurses began a one-day strike Thursday at 34 Northern and Central California hospitals in what was one of the largest such labor actions in years. Hospitals across the Bay Area brought in replacement workers and remained open, though many elective surgeries were postponed. Nurses could be seen on hospital picket lines across the region, waving signs and urging passing motorists to honk and shout in support of their cause. The president of the largest labor federation in the nation joined striking nurses on a Berkeley picket line. He criticized corporate hospital leaders for what union members say are 200 proposed cutbacks by Sutter Health in employee benefits and patient services. AFL-CIO President Richard Trumka took the stage at the Alta Bates Summit Medical Center campus as the picket line swelled to about 200 nurses carrying signs and chanting "chop from the top."