Human rights campaign group Liberty is targeting retailers that are testing Radio Frequency Identification (RFID).
The technology allows product to be tracked through its life, and the campaigners say it represents an invasion of privacy.
Marks & Spencer and Tesco are testing the system, but Liberty communications manager Barry Hugill said: 'We believe that RFID is much too powerful for stores to use. It shouldn't be left to retailers to decide how this system should be used on customers.'
A M&S spokeswoman said: 'We will not do anything to damage the relationship of trust we have with our customers.'