"President Obama promised my patients that they could keep me. But what if because of this new healthcare law, I can't keep them?" Siems tells the camera.
"I've looked at this law. I know the consequences: delayed care and worse yet — denied care," she says.
The ad began airing Wednesday. It will run in the swing states of Virginia, Wisconsin, Iowa and New Hampshire, as well as in New Mexico and Minnesota.
CWA President Penny Nance said the $6 million buy shows the group's members "mean business."
"We know the healthcare issue resonates with people across the country and it's important for them to know the truth about the president's healthcare law," she said in a statement.
"President Obama promised Americans they would be able to keep their coverage and their doctor, but that promise has been broken."
The Obama administration continues to praise aspects of the law as they take effect for expanding care.
On Wednesday, the Department of Health and Human Services touted $128.6 million in new grants to local community health centers for helping to create jobs.