Americans United for Change, AFSCME and the SEIU are up with a small ad buy claiming Sens. Scott Brown (R-Mass.) and Dean Heller (R-Nev.) and Rep. Denny Rehberg (R-Mont.) want to cut Medicare.

"If you cut my Medicare, Sen. Heller, I'll remember it every time I visit my doctor. I'll remember you cut Medicare and Medicaid every time I fill a prescription," says the narrator, an older woman, in one version of the ad. "I'll remember you cut Medicare every time I fall or get hurt. I'll remember you protected millionaires over protecting my health. My friends will remember it, too — all of them. Call Sen. Heller. Tell him to protect Medicare and Medicaid."

All three Republicans are in tight Senate races. Heller voted for House Budget Chairman Paul Ryan's (R-Wis.) budget, which would both privatize Medicare and cut tax rates for top earners. Rehberg and Brown were two of a handful of Republicans who voted against the budget, though Brown initially praised the plan. Democrats and unions believe they can gain major traction on the issue.

National Republican Senatorial Committee communications director Brian Walsh pushed back against the ads' message, arguing that the half-trillion dollars Democrats shifted out of Medicare to pay for their health insurance overhaul undercuts their argument.

"The irony of this pathetic attack ad is that in each of these three races, it’s actually the Democrat candidates who are all firmly on record supporting the $500 billion in Medicare cuts that were included in their massive healthcare overhaul," said Walsh. "The big labor unions funding this ad know that, but yet they are doing everything they can to mislead voters in Montana, Nevada and Massachusetts."

The ad buys are in the low five figures and are running in Boston, Reno, Missoula and Billings.

Watch the Heller ad here:

This post was last updated at 9:05 a.m. to accurately describe Rehberg's and Brown's votes on the Ryan budget.