Almost 1.5 million Florida residents, more than 1 million Texas residents and more than 500,000 North Carolina residents alone get Obamacare subsidies to help pay for their monthly insurance premiums for HealthCare.gov-sold plans, she said.
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"Those who support this lawsuit believe that the law should be dismantled or repealed and they are content to roll back the progress that we have achieved together," Burwell said.
But she also said, "We are confident that we will prevail in the court case argued last week before the Supreme Court."
"The law is clear. The text and structure of the Affordable Care Act demonstrate that individuals in every state are eligible for tax credits," Burwell said.
But plaintiffs in the case and other Obamacare opponents say that the ACA, as written, only allows tax credits for customers of state-run exchanges, because the law only explicitly mentions those subsidies being given to such customers. The law does not explicitly say anything about those subsidies being awarded to customers of a federal exchange.
HealthCare.gov was set up to serve people in states that opted not to create their own Obamacare marketplaces. The Obama administration and its supporters say the contemplation of such a scenario by the ACA gives the administration the ability to issue tax credits for HealthCare.gov's customers.
Without those subsidies, few insurers would be inclined to list their plans for sale on the federal exchange, and few customers would be likely to buy those plans, Obamacare defenders argue.
The Supreme Court is expected to rule on the case in late June. Insurance experts agree that if the subsidies are taken away, millions of people will drop their HealthCare.gov plans because they won't be affordable at retail prices, and the remaining customers will face sharply higher premiums next year as insurers adjust for the exodus of many young, health enrollees.