In addition to the usual price increases to keep up with medical inflation, many insurers are demanding higher rates because of the possibility that President Trump might take away the subsidies known as cost-sharing reduction payments. The subsidies compensate insurers for reducing deductibles, co-payments and other out-of-pocket medical costs for low-income people.

Mr. Trump has repeatedly threatened to cut off the payments as a way to force Democrats to negotiate over the future of the Affordable Care Act.

The president can stop the payments because a federal judge ruled last year that the Obama administration had been illegally making the payments in the absence of a law explicitly providing money for the purpose. The Obama administration appealed the ruling, and the payments continue from month to month, with permission from the court. But Mr. Trump could drop the appeal and stop the payments at any time.

In its latest bulletin, the Trump administration said that many state insurance commissioners had allowed insurers to increase rates for 2018 to account for the “uncompensated liability” that they might face for the cost-sharing reductions.

The amount of the increases varies, but many insurers say that prices will be 15 to 20 percent higher next year because they do not know if they will receive the subsidies they are anticipating.