The Washington-based Physicians Committee for Responsible Medicine (PCRM) filed suit in California "to compel the restaurants to warn unsuspecting consumers".
The group said every sample of grilled chicken products from the seven national chains "tested positive for a dangerous carcinogenic compound called PhIP" during analysis at an independent laboratory.
PhIP is one of a group of carcinogenic compounds called heterocyclic amines (HCAs) that are found in grilled meat. In 2005, the US government officially added HCAs to its list of cancer-causing agents, the doctors' group said.
"Grilled chicken can cause cancer, and consumers deserve to know that this supposedly healthy product is actually just as bad for them as high-fat fried chicken," PCRM president Neal Barnard said in a statement.
"Even a grilled chicken salad increases the risk of breast cancer, prostate cancer and other forms of this lethal disease," he said.