BOISE, Idaho — Federal officials say Idaho’s move to let companies offer health insurance plans that don’t meet Affordable Care Act standards is illegal.

Centers for Medicare and Medicaid Services Administrator Seema Verma issued a letter to Idaho Gov. C.L. “Butch” Otter and Idaho Department of Insurance Director Dean Cameron on Thursday, reminding officials that the Patient Protection and Affordable Care Act remains the law and that CMS has a duty to enforce that law.

Otter, Cameron and Lt. Gov. Brad Little announced earlier this year that they would begin allowing insurers to offer plans that don’t meet all ACA regulations, such as by charging people more based on their health history, or by not covering some health needs like maternity care.

In the letter, Verma said such a move would force CMS to enforce the provisions of the Affordable Care Act on behalf of the state. That could include fining insurance companies $100 a day for every person they insure on a non-ACA compliant plan.