New York State has banned United Healthcare's managed care plan, an arm of the nation's second-largest health insurer, from signing up most types of new customers. State regulators say they took the rare action because the company has persistently defied state rules.

For at least three years, United Healthcare has repeatedly filed late, incomplete or inaccurate reports to the state about its finances and subcontracting, and has wrongly denied payment to doctors and other providers, along with a range of other violations, said officials at the State Health Department.

"We've had several years of findings, them doing corrective action plans, but then when we go out again, we have the same findings," Kathleen Shure, director of the department's Office of Managed Care, said yesterday.

State health officials called it very unusual to cut off new business from a health maintenance organization, but they could not say how often it had been done before. The department's enforcement action, in a May 24 letter from Ms. Shure to United Healthcare, has little practical effect because the company had largely stopped enrolling new customers, anyway, shifting most of its business to two other insurers owned by the same parent company.

The state estimates that United has about 100,000 enrollees in New York.

United is the only large insurer that the department frequently fines for rules violations, officials said — more than a dozen times over the last five years, with more pending — but state law limits each fine to $2,000, no more than a minor annoyance for a large company. The department said that it was still contemplating other penalties, and that the state attorney general's office and the state's Insurance Department — which can seek penalties of their own — are also investigating United.