Another one of California’s largest health insurers has stunned individual policyholders with news of huge rate increases -- this time it’s Blue Shield of California seeking hikes of as much as 59% for tens of thousands of customers March 1.

Blue Shield’s plan comes less than a year after Anthem Blue Cross tried and failed to raise rates as much as 39% for about 700,000 California customers.

San Francisco-based Blue Shield said the increases were the result of fast-rising healthcare costs and other expenses resulting from the new healthcare laws passed last year. “We raise rates only when absolutely necessary to pay the accelerating cost of medical care for our members,” the company told its customers last month.

In all, the insurer said that 193,000 policyholders would see increases averaging 30% to 35%, the result of three separate rate hikes since October that have been rolled into one for about 7,000 members.

Nearly one-quarter of the affected customers -- 44,000 -- will see cumulative increases of more than 50% over five months.

Blue Shield notified some policyholders of the rate increases in late December. That’s when Michael Fraser, a longtime Blue Shield policyholder from San Diego, learned that his monthly bill would climb 59%, to $431 from $271.

“When I tell people, their jaws drop and their eyes bug out,” said Fraser, 53, a freelance advertising writer. “The amount is stunning.”

The increases prompted complaints to new Insurance Commissioner Dave Jones, criticism on the Internet and letters to The Times. They are providing an early test for Jones, a former Democratic state assemblyman who targeted Anthem last year after it sought its big increases. . . .