Due to increasing consumer skepticism towards promotional messages, companies are looking for new ways to communicate with their target audiences in a less obtrusive way than traditional advertising. Sponsored content disseminated on the online portals of newspapers (i. e., online advertorials) is regarded as a promising way to promote products and brands. Regulations require communicators to inform consumers about the commercial nature of this ‘masked’ persuasion attempt by including an explicit sponsorship disclosure (i. e., a ‘Sponsored’ label). This study demonstrates that such an explicit advertising cue may not be enough to alert recipients. Furthermore, this study investigates the effects of promotional messages by means of a 2 (no disclosure vs. disclosure) x 2 (no forewarning vs. forewarning) experiment. Results show that both (i) foregoing instructions aimed at activating consumers’ persuasion knowledge (i. e., an additional forewarning message) and (ii) recipients’ prior media literacy can foster the effect of sponsorship disclosures in triggering situational distrust towards brand-related content, and in turn, increasing consumers’ reactance.