Although new regulation in Belgium (July 2023) prohibits nearly all forms of gambling advertising, gambling brands already started to shift their advertising budgets to marketing forms that are not strictly regulated and can be considered loopholes or grey areas. One concerning shift is the one to cause marketing, which refers to gambling brands sponsoring charities or prosocial causes and communicating about these partnerships. This is concerning due to the image transfer that may occur, which refers to the transfer of associations people have with charities, such as compassion, generosity and kindness, to gambling brands. Relying on gambling sponsorship theory and legitimacy theory, I will investigate the role of consumer legitimacy in consumers’ responses to cause marketing initiatives by gambling companies. In particular, I will examine the impact of exposure to cause marketing on gambling-related, brand and cause outcomes, the explanatory mechanisms, and the moderating roles of cause marketing strategy, organizational status of the gambling company and consumers’ gambling profile. A multi-method approach combining qualitative research (i.e., in-depth interviews), experimental research and theory-building will be conducted. The current regulatory situation regarding gambling advertising in Belgium is exceptional and therefore watched with great attention, whereby research on the implications of such strict regulation on gambling advertising is urgent and innovative.