In ads running in Washington, D.C., and North Dakota newspapers, the Coalition to Stop Gun Violence calls on Heitkamp's constituents to push her to support gun control.
The ads are signed by the parents of children killed at the Virginia Tech, Tucson and Aurora shootings.
"No parent should have to send their children to school wondering if they will come home," it reads.
Heitkamp said on ABC News this Sunday that "I think you need to put everything on the table, but what I hear from the administration ... that's way, way in extreme of what I think is necessary or even should be talked about. And it's not going to pass."
The White House is said to be interested in pursuing a more expansive gun-control agenda than just banning assault weapons and high-capacity ammunition. A story in the Washington Post on Sunday said the administration was also looking at a national database to track the sale and movement of guns, as well as universal background checks.
Heitkamp, who comes from a deep-red state and barely eked out a win over her Republican opponent, former Rep. Rick Berg (N.D.), received an "A" rating from the National Rifle Association and is a supporter of gun rights.
The ads are running in Roll Call and Politico, in Washington, on Tuesday, and will run in the Fargo Forum and the Bismarck Tribune, in North Dakota, on Wednesday.
"Tell Senator Heitkamp it's time for her to stand up for America's families, NOT the gun lobby," it closes, with instructions to call her Washington office.