The Trump administration on Wednesday started sending $500 refunds to Obamacare enrollees whom the White House said were overcharged for healthcare by the Biden administration.

The Treasury Department is releasing these refund checks to more than 950,000 Americans in 30 states, according to an administration official. Some families with more than one "affected person" will receive multiple $500 checks or direct deposits, the official said.

Recipients will also receive a letter dated Sept. 30 from President Donald Trump, which is being mailed starting Thursday, the official said.

"For years, the Biden Administration overcharged you to fund the operation of HealthCare.gov," Trump writes in the letter, which CNBC viewed.

The White House announced earlier this month that it would begin issuing refunds in October.

Jonathan Oberlander, a professor of health policy and political science at the University of North Carolina at Chapel Hill, told CNBC earlier this month that the policy is likely a form of "damage control" for the White House to distract from higher healthcare costs.

"This announcement is less about health policy and much more about the 2026 Congressional elections," he wrote. "It's part of a broader effort by President Trump to buy continued Republican control of the House and Senate via promises of direct government payments to voters."

Health policy experts said a $500 refund does little to offset ACA premiums that, in many cases, rose by several thousand dollars per year for enrollees who had previously received enhanced subsidies.

The 30 states that will receive the Obamacare refunds are: Alabama, Alaska, Arizona, Arkansas, Delaware, Florida, Hawaii, Indiana, Iowa, Kansas, Louisiana, Michigan, Mississippi, Missouri, Montana, Nebraska, New Hampshire, North Carolina, North Dakota, Ohio, Oklahoma, Oregon, South Carolina, South Dakota, Tennessee, Texas, Utah, West Virginia, Wisconsin and Wyoming.

These states use the federal ACA exchange, while the others use their own state-run marketplace. The latter tend to be governed by Democrats, according to health policy experts.

The largest number of refunds will be issued in Texas and Florida, where 139,000 and 127,900 people will get refunds, respectively, according to federal data shared with CNBC.

The primary recipients of the refunds will be people whose income is over 400% of the federal poverty line, the Trump administration official said. That's roughly $63,000 for an individual and $129,000 for a family of four.

These individuals lost all federal premium assistance when the enhanced subsidies disappeared this year.

However, "some people" between 100% and 400% of the poverty line will also receive a refund, the official said.

The $500 refunds are being paid from a "surplus" of "user fees" collected by the Biden administration, according to the Trump administration official. The White House said these excessive charges had been passed on to consumers during the Biden era through higher health insurance premiums.

The Centers for Medicare and Medicaid Services collects user fees from health insurers who participate in the ACA marketplace. Under Obamacare, healthcare exchanges can collect user fees from insurance companies to help fund ACA marketplace operations.

The fees went up and down during the Biden administration in different years — and were at times lower during the Biden era than during the first Trump administration, Oberlander said.