CASPER, Wyo. (AP) — The Northern Arapaho tribe filed a federal lawsuit Tuesday alleging that proposed Internal Revenue Service rules could cause Native Americans to pay higher insurance premiums or lose health care benefits.

Tribal leaders said the recently proposed IRS interpretation of the large-employer mandate would unlawfully exempt Native Americans working for the tribe from receiving tax credits and cost-sharing benefits specifically outlined by new federal health laws.

Northern Arapaho Business Council members said the IRS rule would eliminate tribal tax credits for health care benefits and make those earning more than 300 percent of the federal poverty level exempt from cost-sharing provisions that currently cover Native American insurance premiums.

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

The Northern Arapaho Tribe has about 10,000 enrolled members and shares a large reservation in Wyoming, southeast of Grand Teton National Park. It employs more than 600 people.

The tribe insures its workers with plans from the federal health insurance marketplace and provides more than 80 percent of premium costs, the Casper Star-Tribune reported (http://tinyurl.com/p6v475o).

Under the rule, tribal governments and agencies are considered large employers. Those Native Americans employed by the tribes would be subject to provisions of the large-employer mandate. More than 62 percent of Northern Arapaho members live below the poverty line.

If approved, the rule would take effect Jan. 1. The rule-making is on hold, awaiting results of the case, filed in the U.S. District Court of Wyoming.

The tribe said Congress did not intend the health care legislation to block Native Americans' benefits and that the IRS rulemaking exposes a rift between legislation and the executive branch.

The IRS referred calls to the Department of Justice, which did not immediately respond to a request for comment Wednesday.

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Information from: Casper (Wyo.) Star-Tribune, http://www.trib.com