Health insurer Cigna Corp. won’t be able to sign up new customers for its private Medicare plans during the fall enrollment season this year because of an investigation by U.S. regulators.

The Centers for Medicare and Medicaid Services said in January that it found “widespread and systemic failures” in Cigna’s private Medicare business. On Tuesday, the Bloomfield, Connecticut-based insurer said in a regulatory filing that it probably can’t fix the problems in time for the enrollment season for private health insurance and drug coverage plans, which starts next month.

As of June 30, Cigna had about 533,000 customers in its Medicare plans, known as Medicare Advantage, and 1.04 million in its drug plans, known as Medicare Part D, the company said on its website. The privately run insurance plans are sold as alternatives to the government-run version of the health program for the elderly and disabled, and the drug benefit was created in 2003 to supplement health coverage.