Washington ? The Supreme Court ruled Wednesday that states can pass laws forcing HMOs to open their networks to more health care providers, giving patients broader choices of doctors and hospitals but potentially boosting costs.

The unanimous ruling was a setback for the managed care industry, which argued that closed networks lower health care costs because providers agree to accept lower fees in return for a guaranteed stream of patients.

The decision also gives states more freedom to regulate insurance companies, another in a line of decisions from the court expanding states’ rights.

About half the states have passed “any willing provider” laws in the past decade in response to complaints that HMOs and insurance companies sometimes block people from seeing the doctors of their choice.

The laws require managed care networks or insurance companies to accept out-of-network health care providers — physicians, pharmacists, nurse practitioners or specialists. In return, the providers must agree to the insurer’s reimbursement rates and contract terms.

The court ruled on a challenge to Kentucky’s laws, considered the broadest in the country. The Bush administration had sided with Kentucky.

“It’s a message to states that you can have consumer protection laws,” Kentucky Insurance Commissioner Janie Miller said.

Industry lawyers had told the court that the laws increase administrative costs, make it harder for HMOs to monitor quality and jeopardize deals that health plans have made with providers.

Karen Ignagni, president of the American Association of Health Plans, which represents more than a thousand health maintenance organizations and other plans, said the Kentucky laws drove up patients’ health care expenses. In court filings, justices were told that in states with willing provider laws, studies found 15 percent increases.

The Kentucky statutes were challenged by a group of HMOs and an industry trade association. The case turned on whether the laws regulate insurance, which states are allowed to police, or regulate employee benefits, an area reserved for Congress.

Other states with any willing provider laws, are Alabama, Connecticut, Delaware, Georgia, Idaho, Illinois, Indiana, Massachusetts, Minnesota, Mississippi, New Hampshire, New Jersey, North Carolina, North Dakota, South Dakota, Tennessee, Texas, Wisconsin, and Wyoming. In addition, Arkansas and Louisiana have laws that have been blocked by courts, and Florida and South Carolina repealed their laws.