NASHVILLE, Tenn. — BlueCross BlueShield of Tennessee is withdrawing from the Affordable Care Act marketplace in the Memphis, Nashville and Knoxville regions. In a news release, the company says the change will affect an estimated 100,000 Tennesseans.

The decision comes a month after Tennessee officials approved an average rate increase of 62 percent for the insurer.

“BlueCross committed early to the ACA Marketplace and has been the only health insurer to offer coverage options in every region in the state since 2014,” according to the news release from the company. “And we have experienced losses approaching $500 million over the course of three years on ACA plans, which is unsustainable.”

BlueCross BlueShield of Tennessee will continue selling ACA plans in other regions of the state. The change will not affect seniors with Medicare Advantage plans, those enrolled in BlueCare or anyone who has insurance through an employer.

The Chattanooga-based insurer says it has concerns about uncertainties with the Affordable Care Act at the federal level, but it will continue to evaluate the ACA marketplace, including a possible return to offering plans statewide in 2018.

In a statement to the media, state Senate Republican Leader Mark Norris blamed the federal government for the company’s withdrawal from the three regions. He cited the failure of some health insurance co-ops after Congress stopped the Obama administration from covering their losses and said it shows “why Medicaid expansion in Tennessee was always an intolerable risk.”

But Democratic U.S. Rep. Jim Cooper laid the blame for the ACA marketplace’s problems on Tennessee’s decision not to expand Medicaid through a plan called Insure Tennessee.

“The health care exchanges are working in many other states, but our state is turning down billions of dollars that would stabilize our health insurance market,” Cooper said in a statement.