Large carriers are pouring millions into a campaign to thwart Proposition 45, a proposal backed by the California insurance commissioner that would create a powerful oversight on rate increases.

In the last week, carriers pumped another $12 million into the anti-Prop 45 campaign, raising the total spent on those efforts to $55.4 million, according to the state. The pro-45 advocacy group Consumer Watchdog Campaign — a coalition of consumer advocates, nurses, attorneys and policyholders — said opponents are concerned that their expenditures won't sway voters on the issue.

"The big health insurance companies are panicked that the public will learn the truth about their opposition to Prop 45 and support its controls against rate hikes so they are doubling down on their deceptive television advertising campaign to confuse voters," said Jamie Court, president of Consumer Watchdog and author of Prop 45. "The industry is worried that with enough light and air around the election the public will learn the truth that insurance companies are opposed to Prop 45 because it gives California the power 35 other states already have to reject excessive rates."