She described plastic bags as “hideously ugly, gigantically dangerous, and outrageously expensive.”
Employees of plastic bag manufacturers protested against the ban, some wearing T-shirts saying “Don’t Kill My Job”.
Alejandro Ortega, who works for manufacturer Crown Poly, said: “My family depends on my job.”
Several other cities in California, including San Francisco, have already adopted measures against plastic bags.
The state of California uses an estimated 12 billion plastic bags each year and less than 5 per cent are recycled.