Attorney General Bob Ferguson today joined a “friend of the court” brief opposing a lawsuit that threatens health care coverage gains under the Affordable Care Act (ACA).

In a case before the United States Court of Appeals for the District of Columbia Circuit, plaintiffs are arguing that the ACA does not allow the federal government to provide tax credits to people buying health insurance in states participating in the federal insurance exchange established by the act.

These tax credits are crucial for low- and middle-income people to purchase affordable health insurance.

“This lawsuit threatens access to affordable health insurance in every state, not just those using the federal exchange,” Ferguson said. “With an adverse judgment, health coverage for thousands of Washington residents would be in jeopardy.”

If the plaintiffs in Halbig v. Burwell are successful, key provisions of the ACA could be made unworkable, throwing the future of the act into question. Washington created its own exchange, but joined this amicus brief to protect its residents’ access to affordable health insurance.

Attorneys general from 18 states have signed onto brief. The list includes Washington, Virginia, Arkansas, California, Delaware, Hawaii, Illinois, Iowa, Maine, Maryland, Mississippi, New Hampshire, New Mexico, New York, North Carolina, Oregon, Pennsylvania and Vermont.