Big health insurer Anthem said Wednesday that it won’t sell Obamacare plans to new customers in most of Maine in 2018 — and current customers will lose federal aid that reduces coverage costs if they stick with Anthem.

The company as it has done in announcing departures from a number of other states’ individual health plan markets in recent months, cited a “volatile” individual market that is “shrinking and deteriorating.”

Anthem also pointed to the “continual changes and uncertainty in federal operations” ever since the Trump administration assumed oversight of Obamacare, a program that the White House strongly opposes.

One of the biggest sources of uncertainty is the Trump administration’s refusal to guarantee permanent continuation of billions of dollars worth of reimbursements to insurers for discounts that insurers must offer many Obamacare customers by law.

Anthem’s decision, which came on the day of the deadline for insurers to sign contracts for Obamacare plans in 2018, will leave Maine with just two insurers selling plans widely when open enrollment starts Nov. 1.

The company has been selling such plans statewide to people who do not get health coverage through a job, Medicare, Medicaid or other source.

Anthem said it will not sell new customers plans next year through, the federally run Obamacare exchange that serves Maine and most other states.

The insurer also won’t sell almost all of the plans it now sells outside of that exchange in Maine. Anthem will continue offering employer-based health coverage.

Low- and middle-income people who buy individual health plans can get federal subsidies to reduce both their monthly premiums and out-of-pocket health costs only if they buy coverage through or a state-run Obamacare marketplace. People who buy coverage off-exchange cannot get such financial aid.

Most of the more than 79,000 Maine residents who signed up for a plan from Anthem and two other insurers selling coverage through this year qualified for such aid.

Maine has a guaranteed renewal law that mandates customers be allowed to renew with their current insurer if that insurer is not completely exiting a market.

That will allow current Anthem customers who now buy plans via to keep their existing coverage in 2018.

“But these plans will be offered off-exchange, and they will not be eligible to receive financial assistance or subsidies,” Anthem said in a prepared statement.

In addition to allowing existing customers to renew their coverage, albeit off-exchange, Anthem will sell just a single “gold-level” plan off of the federal exchange in only three counties. Gold plans cover, on average, 80 percent of their customers’ medical costs, with individuals being responsible for the remaining share.

By maintaining a small toehold in Maine’s individual health plan market, Anthem will keep open the option of returning to that market on a wide scale in 2019. If it did not keep that minimal presence, the insurer would be blocked from returning to the Obamacare market for five years.

Anthem said it will monitor changes in the individual market, and “We will reevaluate whether a more robust presence in the exchange is appropriate in the future.”

The company in the past several months has announced full-scale or partial departures from Obamacare markets next year in California, Georgia, Missouri, Ohio, Indiana, Wisconsin, Nevada and Virginia.

In its statement about Maine, Anthem said, “While we are pleased that some steps have been taken to address the long term challenges all health plans serving the individual market are facing, the market remains volatile.”

“A stable insurance market is dependent on products that create value for consumers through the broad spreading of risk and a known set of conditions upon which rates can be developed,” the insurer said.

“Today, planning and pricing for ACA-compliant health plans has become increasingly difficult due to a shrinking and deteriorating individual market, as well as continual changes and uncertainty in federal operations, rules and guidance, including the restoration of the health insurance tax on fully insured coverage and continued uncertainty around the future of cost sharing reduction subsidies.”