“The individual mandate is inextricably linked to the insurance-market reforms included in the health-care-reform law," said Robert Zirkelbach, a spokesman for the industry group America's Health Insurance Plans. There are historical precedents for trying to overhaul the insurance system without mandates in the states, and those precedents are failure.

"In the 1990s, several states enacted insurance-market reforms without achieving broad participation and it failed," Zirkelbach said. "Premiums increased dramatically, consumers and employers had fewer coverage choices, and the number of uninsured increased." To avoid "repeating the state experience," the 2010 health-insurance overhaul mandated that everyone purchase coverage and established a long initial open-enrollment period "to incentivize young, healthy people to purchase and maintain health insurance rather than waiting until after they get sick or injured to sign up." Without these young people purchasing insurance in the markets, the whole pricing structure of the private health plans in the new markets goes haywire.

Even delaying the mandate past the March 31 deadline, which may sound intuitively like a fair thing to do, would fundamentally disrupt the markets in a way that increases costs, insurers warn. Everything insurers have done was designed around a fixed plan, and any significant changes in mid-course—and we are now in mid-course—will destabilize what's being rolled out this year and for 2015 (open enrollment for 2015 will take place in late 2014).

“The administration’s proposal to align the individual-mandate penalties with the open-enrollment sign-up period ending on March 31 is consistent with what health plans assumed in their premiums for next year. Going beyond this proposal by delaying the individual mandate and/or extending the open enrollment period past March 31 could have a destabilizing effect on insurance markets, resulting in higher premiums and coverage disruptions for individuals and families," Zirkelbach said.

“Moreover, if these vital enrollment incentives were to change, the premiums health plans filed for next year would have to increase to account for fewer young and healthy people signing up for coverage.”

Health and Human Services Secretary Kathleen Sebelius pointed out during the House Energy and Commerce hearing Wednesday that the open-enrollment period being offered consumers by the exchanges is already "extraordinarily long."

"It's about six times as long as a typical generous open-enrollment period," she said. "And it's important for the insurance partners to know who is in their pool so again they can stay in the market next year and know who they are insuring."

If Healthcare.gov is fixed by November 30, the administration's stated target, customers will have four full months to enroll, she noted.