Those groups have run ads in other markets, too, like Washington, D.C., and one in Montana targeting Democratic Sen. Max Baucus.
In the groups' Nebraska ad, restaurant owner Mike Snider of Ralston, Neb., asks Nelson not to delay health care reform.
Nelson was one of six senators who penned a letter last month calling for Congress to take its time in crafting a reform plan.
He is considered a potential swing vote, having voiced criticism of some Democrat-backed proposals, particularly a so-called public option that would create a government-run insurance plan to compete with those offered by the health insurance industry.
"Like too much stuff that comes out of Washington, it's hard to know what's fact and what's fiction," Nelson says in his ad. "Any plan must keep spending under control, help small businesses, improve care, control costs, and most of all, the plan needs to work for Nebraska."
Nelson's 2012 campaign committee paid for the ad. His spokesman, Jim Fagan, said Tuesday he could not say how much was spent on the ad.
University of Nebraska at Omaha political science professor Randall Adkins said it is becoming more common for interest groups to target individual lawmakers - even lawmakers within the group's own party.
"There are a lot of Democrats in traditionally conservative districts," Adkins said. "I don't think it has a whole lot to do with Sen. Nelson's politics; I think it has a whole lot more to do with the district from which he comes. Nebraska tends to be a lot more conservative."
