Central New York’s biggest Obamacare insurer expects consumers to drop health coverage in droves in 2019 when a federal mandate requiring individuals to buy insurance or pay a tax penalty is repealed.

Fidelis Care anticipates the number of people buying coverage in New York’s individual insurance market will shrink by 37 percent next year, driving up medical costs 23 percent, according to documents the company filed with the state.

That’s a major reason Fidelis is asking the state to let it increase premium rates in 2019 by a whopping 39 percent.

The proposed rate hike is significantly higher than increases requested by other New York insurers. Excellus, MVP and CDPHP, insurers that also sell Obamacare policies in Central New York, have all asked for increases of less than 10 percent. Statewide, 14 insurers in the individual market have asked for increases averaging 24 percent.

The state, which usually gives insurers less than they request, is expected to make a decision on the rate hike requests later this summer.

The proposed increase by Fidelis could have a big effect on the more than 6,000 Central New Yorkers enrolled in individual Obamacare plans offered by Fidelis. The company controls 60 percent of the individual insurance market in Central New York and 41 percent statewide. Federal tax credit subsidies could reduce 2019 premium increases for consumers eligible for the subsidies.

Most Central New Yorkers get coverage through employers.

The Trump administration repealed the individual mandate, the most unpopular feature of the federal Affordable Care Act, also known as Obamacare.

The mandate was designed to prevent dramatic rate increases by making sure the insurance market has enough young health people to offset older, sicker people with higher health care costs.

Not all insurers expect the repeal of the individual mandate to have as profound an effect on the state’s individual insurance market as Fidelis does. CDPHP and Healthnow, for example, said in their rate filings it will have no effect. Excellus is seeking an 8.9 percent increase, but said it would have only asked for a 1.6 percent increase without the appeal.

Fidelis said its proposed increase is about three times higher than it would be without the repeal.

“We’ve never seen before what happens when an individual mandate goes away,” said Bill Hammond, health policy director of the Empire Center, an Albany think tank.

He said insurers are making educated guesses about the impact of the repeal and the forecast by Fidelis is the most pessimistic. Hammond said Fidelis has a lot of young, healthy members.

Without an individual mandate, New York’s individual insurance market may go back into a “death spiral” like it did before the advent of the federal Affordable Care Act, also known as Obamacare, Hammond said.

Before the individual mandate, most people did not buy individual coverage in New York until they got sick, while many young, healthy people went without insurance. Premium rates more than tripled while the number of people buying individual coverage plummeted. By 2013, the year before Obamacare took effect, New York had the nation’s highest insurance rates.

“When the individual mandate goes away, it may be the healthier customers who are first to go because they have the least to lose from going without coverage,” Hammond said.

Fidelis, a health plan affiliated with the Catholic church, is in the process of being sold for $3.75 billion to Centene Corp., a public company that trades on the New York Stock Exchange. The sale is expected to close July 1.

In a statement, Fidelis said Centene had no input in its 2019 rate hike request.