A secretive “dark money” group, which claims to represent doctors and patients, engaged in a TV advertising blitz totaling at least $2.3 million from late July through mid-August. Its ads urge vulnerable senators to reject a proposal meant to cut down on expensive surprise medical bills.

Doctor Patient Unity, an obscure group that doesn’t list its members or disclose its funding, was incorporated in Virginia on July 23. Just a few days later, it ran its first TV ads during CNN’s broadcast of the Democratic presidential debate, a preview of the multi-million dollar ad blitz that would soon follow.

The TV ads, which aired in nearly a dozen states, key in on one of America’s top healthcare issues: unexpected medical bills. The answer, the group says, is not a government-imposed limit on the amount of money health care providers can charge to some out-of-network patients — a proposal that appears primed to pass the Senate.