At risk is the Pre-Existing Condition Insurance Plan, a transition program that's become a lifeline for the so-called "uninsurables" — people with serious medical conditions who can't get coverage elsewhere. The program helps bridge the gap for those people until next year, when under the new law insurance companies will be required to accept people regardless of their medical problems.

In a letter this week to Health and Human Services Secretary Kathleen Sebelius, state officials said they were "blindsided" and "very disappointed" by a federal proposal they contend would shift the risk for cost overruns to states in the waning days of the program. About 100,000 people are currently covered.

"We are concerned about what will become of our high risk members' access to this decent and affordable coverage," wrote Michael Keough, chairman of the National Association of State Comprehensive Health Insurance Plans. States and local nonprofits administer the program in 21 states, and the federal government runs the remaining plans.