"Last year a lot of promises were made regarding healthcare reform, but America's seniors knew forcing a bill through Congress when Americans overwhelmingly opposed it would be disastrous — and they were right," says the group's spokesman, country singer Pat Boone, in the ad.

The ad says the Democratic health insurance reform law cut $500 billion from Medicare and creates a board of 15 "unelected, unaccountable bureaucrats."

Boone then says the board "can ration care and deny certain Medicare treatments so Washington can fund more wasteful spending," and that Medicare will be bankrupt in nine years.

Democrats pushed back against the group's characterization of their votes. "The 60 Plus Association is spending millions of dollars to distract voters from the Republican plan to privatize Medicare that would make seniors pay thousands more for their coverage," said Democratic Senatorial Campaign Committee spokesman Matt Canter. "Independent fact checkers have already denounced this ad, and it is no coincidence that this new false attack comes just weeks before Republicans issue another budget that would end Medicare."

Jim Martin, the head of the 60 Plus Association, told The Hill that the organization was spending $1.1 million against Nelson, $850,000 against Stabenow, $720,000 against Brown, $450,000 against McCaskill and $350,000 against Tester.

Watch one version of the ad here:

This post was updated at 12:35 p.m.