WASHINGTON, D.C. - The federal government on March 7 responded to a letter filed in the District of Columbia Circuit U.S. Court of Appeals by plaintiffs in a case challenging an Internal Revenue Service regulation imposed under the Patient Protection and Affordable Care Act (ACA) that extends eligibility for premium assistance subsidies to people who purchase health insurance through exchanges established by the ACA. The plaintiffs' letter addresses a bulletin issued by the Center for Medicare and Medicaid Services (CMS) discussing the tax credits available for individuals who purchase health care coverage through exchanges (Jacqueline Halbig, et al. v. Kathleen Sebelius, et al., No. 14-5018, D.C. Cir.).