Yet about 83% of the comments are identical to a letter that appeared on the website of a secretive advocacy group called Medicare Advantage Majority, a data analysis by KFF Health News has found.

The “dark money” group does not reveal its funders or much else — other than to say it is “dedicated to protecting and strengthening Medicare Advantage” and is “powered by hundreds of thousands of local advocates nationwide.”

“Our campaign provides information and offers tools for concerned Americans to use to reach decision makers,” spokesperson Darren Grubb said in an email.

There’s no doubt health insurers are unhappy with a January proposal from the Centers for Medicare & Medicaid Services, or CMS to keep Medicare Advantage reimbursement rates essentially flat in 2027 — far less than they expected from the Trump administration.

Medicare Advantage plans differ from traditional Medicare because private insurance companies administer them.

“The proposed rate plan ‘puts my access to care at risk,’ the group’s template letter to policy makers reads in part.

Critics warn that these sorts of campaigns may create a misleading impression of grassroots support, especially when it’s not clear who is financing them.

Some health care policy experts believe industry groups or their surrogates routinely overstate possible negative impacts of rate decisions they don’t like.

“It is legitimate for people to be worried,” said Julie Carter, counsel for federal policy at the Medicare Rights Center, a group that advocates for older adults and people with disabilities.

People struggling to pay health care bills may have little use for the policy debate in Washington.

“If it wasn’t for being able to have this program, I really wouldn’t be able to afford any kind of medical services, to be honest,” said EsterAlicia Rose, 75.

Kathy Lovely-Marshall, 66, a retired nurse who lives in Brookville, Ohio, receives “a lot of perks” from her plan.

But Corenia Branham, 90, a widow and cancer survivor who lives in Alum Creek, W.Va., said she wants nothing to do with Medicare Advantage plans run by private health insurance companies.

Grubb, the Medicare Advantage Majority spokesperson, disputed that account.

Other Medicare Advantage advocacy groups have stepped up ad campaigns as the rate decision looms.

As of March 11, CMS said it had received 46,884 comments but had posted only 16,324 online.

“The agency focuses on reviewing the substance of timely submissions and does not speculate on volume, sentiment, or potential impact of comments while the comment period is open/under review,” said CMS spokesperson Catherine Howden.

KFF Health News is a national newsroom that produces in-depth journalism about health issues.