Seventy-two members of the Stationary Engineers Local 39 are walking picket lines at all four CPMC campuses in San Francisco.
They have been working without a contract since October of 2010 and finally decided to strike after negotiations broke down.
"All the other Sutter hospitals have gotten a deal with the Local 39, and the CPMC hospitals which is the richest of the Sutter hospitals, is trying to undercut all the other deals that they have," said Joe Klein of Stationary Engineers Local 39.
Kathie Graham, spokesperson for CPMC, said: "We have some differences, but we're hoping that the membership will ask their leaders to go back to the table so we can resolve this through negotiations."
CPMC officials don't expect the strike to disrupt hospital services.
The workers plan to stay out until the company offers them a contract similar to other engineers in the Sutter Health Care Group.