Over the past few years, as teams have refined their ability to team up with other cars to create more speed, drivers and spotters have had the ability to talk to multiple teams over their radios. They used it to coordinate which cars would pair up and to help drivers switch from pusher to pushee. By eliminating such communication, NASCAR hopes teams will have a more difficult time making deals and remaining in pairs. The driver pushing especially needs this communication because he has little to no visibility.
It was so refined that one spotter would communicate for both drivers even if one of the drivers wasn't with his organization. This is racing's latest rule change to address the two-car tandem that surveys indicate fans would like to see eliminated. ESPN