Federal regulators have stopped Cigna from enrolling new Medicare customers until the health insurer deals with problems that have triggered care denials or delays and higher costs for some people. The insurer, which is being acquired by the Blue Cross-Blue Shield carrier Anthem, has a "longstanding history" of not complying with requirements from the Centers for Medicare and Medicaid Services, or CMS, according to a 12-page letter the agency sent to Cigna earlier this week. "The nature of Cigna's noncompliance provides sufficient basis for CMS to find the presence of a serious threat to enrollees' health and safety, supporting the immediate suspension of Cigna's enrollment and marketing activities," the letter stated. Cigna said in a brief regulatory filing Friday that it is cooperating with federal officials and working to resolve the issues as quickly as possible.Read more on NewsOK.com