Victims range from home healthcare patients to pediatric eyewear customers.
The lawsuit alleges that Comcast's new wireless routers increase electricity costs, degrade performance, and subject customers to security risks.
Verizon, however, is continuing to insert the tracking data into its customers' Web traffic.
The campaign targets corporate executives via hotel Wi-Fi networks.
The Electronic Frontier Foundation's Jacob Hoffman-Andrews says AT&T and Sprint may be using similar headers as well.
That's true despite the fact that a third of healthcare employees work outside the office or clinic at least once a week, according to Forrester.