The Northern Arapaho have filed a federal lawsuit aimed at keeping its workers insured under the Affordable Care Act.

The suit argues that an Internal Revenue Service rule improperly requires the Northern Arapaho to provide employer-based health insurance plans to 600 workers, including those working in Tribal government and the Wind River Casino.

The Northern Arapaho Tribe is the largest employer in Fremont County, Wyoming. When the Internal Revenue Service rule goes into effect on January 1, 2015, Tribal businesses will have to comply with the Affordable Care Act’s “Large Employer mandate.”

That provision requires all businesses with more than 50 employees to provide health insurance for their workers. As a result, employees at Tribal businesses would become ineligible to purchase subsidized insurance from companies that list plans on Healthcare.gov, the federal health insurance exchange.

That doesn’t sit well with Northern Arapaho leaders.

“The Northern Arapaho Business Council fully supports what Congress and the President have accomplished with the Affordable Care Act, but the folks in the agencies have taken a wrong turn in implementing it,” said Councilman Darrell O’Neal in a statement.

The Northern Arapaho case was filed in federal District Court in Cheyenne on Dec. 8. It argues that the Affordable Care Act (ACA) does not count tribes as Large Employers, and that Congress didn’t intend for the IRS to view tribes that way because doing so would remove important benefits.

“Congress did not intend to create special benefits for working-class Native Americans, only to have Defendants promulgate regulations that prevent working-class Native Americans who work for Tribes from obtaining those benefits,” the suit states.

Applying the “Large Employer mandate” to Northern Arapaho businesses would preclude workers from buying the ACA’s subsidized insurance plans — which are offered to all Americans who make up to 400 percent of poverty level. (Section §1401 of the ACA.)

The suit further points out that the IRS rule would remove a co-pay exemption provided specifically to American Indians by the ACA. This provision exempts tribal members from making co-pays on treatment if their income does not exceed 300 percent of the poverty level. (Summary of section §1402(d) of the ACA.)

“Congress created these benefits for working-class Native Americans and their families,” said Councilman Richard Brannan in a statement. “The IRS overlooked their trust obligations and treaty responsibilities in putting forward these rules that undermine benefits for Native Americans.”

Since the passage of the ACA the Northern Arapaho have counseled their employees to seek coverage from companies that offer plans on the federal health care exchange. The Northern Arapaho tribe currently pays 80 percent of the premiums for Tribal workers who get subsidized coverage under the ACA.

The Northern Arapaho previously offered employer-based plans, but found them more costly.