Aetna announced that it will walk away from more than two-thirds of the ObamaCare exchange markets it participated in this year, dropping from 778 counties to 242 counties next year. Aetna will maintain a presence in just four states, it says – Delaware, Iowa, Nebraska and Virginia – down from 15 states this year. Aetna covered about 838,000 people through the Obamacare exchange in its 15 states as of June 30.

Aetna, the third largest insurance company in the U.S. says the market’s financials are unworkable, pointing out that it has lost more than $430 million since January 2014 on its individual products. It’s not the only major player to walk away from the Obamacare exchanges.

“More than 40 payers of various sizes have similarly chosen to stop selling plans in one or more rating areas in the individual public exchanges over the 2015 and 2016 plan years,” CEO Mark Bertolini said in a statement. “As a strong supporter of public exchanges as a means to meet the needs of the uninsured, we regret having to make this decision.”

Aetna’s announcement comes on the heels of an announcement by Anthem that, in a reversal of expectations, it is now projecting mid-single digit losses on the individual plans it sells on the exchanges. Humana said it would dial back its participation on the exchanges from 15 states to 11 earlier this month. UnitedHealth Group plans to remain on “three or fewer exchange markets,” its chief executive, Stephen Hemsley, said on an earnings call in July. Cigna has said that it is losing money on the exchanges, but the insurer is planning to expand its marketplace presence to three new states in 2017.

Like other insurers, the company blamed its withdrawal on a pool of exchange participants that has turned out to be heavier users of their insurance plans than previously predicted. Insurers need healthy plan members to off set sick patients to balance the books.

The move also comes amid a fight between Aetna and the U.S. Justice Department over the government’s lawsuit attempting to block the company’s acquisition of insurer Humana. The government has said the deal violates anti-trust laws, but Aetna has said it will lower costs and improve choice.

One major issue is the risk pool – the balance of healthy and sick people who incur major medical costs. An analysis by the Centers for Medicare and Medicaid Services released last week showed that the per-month medical costs of members on the exchanges each month had barely budged between 2014 and 2015, suggesting that the risk pool was not getting worse.

Next year will be Obamacare’s fourth of providing coverage in the new markets. Aetna’s decision doesn’t affect people covered by the company this year, but when they look for coverage next year, they’ll need to pick a new insurer. The decision, which affects about 80 percent of Aetna’s customers in individual ACA exchange plans, raises the prospect that some consumers will only have one insurer to choose from when they buy 2017 coverage.

ObamaCare relies on privately run insurers to offer health plans that individuals can buy, often with government subsidies. About 11.1 million people were signed up for Obamacare plans at the end of March.  The workers’ compensation claims industry had believed that the availability of low cost insurance to those who were previously uninsured would reduce the filing of marginal industrial claims.