Italy's market and free competition regulator AGCM said Monday it has put British American Tobacco (BAT) under investigation over the use of social media stars for "covert advertising." Three Italian celebrities, paid by the tobacco giant, urged their Instagram followers to post content with tags and hashtags related to Glo Hyper, BAT's heated tobacco device. AGCM charged that this amounted to hidden -- and illegal-- advertising because there were "no graphic or textual warnings" marking it as a publicity drive. "The general prohibition of hidden advertising has general scope and must therefore also apply to messages spread by influencers on social networks," the regulator said. The three celebrities -- model Stefano Sala, dancer and TV presenter Stefano De Martino, and model, actress and TV presenter Belen Rodriguez -- were also put under investigation. Companies and individuals targeted by antitrust probes can face fines. BAT did not immediately respond to a request for comment on the affair. aa/wai