Amazon has contacted agencies about its $1bn (£760m) global media planning and buying business, putting Initiative on alert. Initiative won Amazon's global media business in 2013.
The ecommerce titan has issued an RFP seeking a media agency to handle promotional campaigns in North America and other markets around the world, according to AdWeek.
Neither IPG Mediabrands nor Amazon responded to requests for comment from Campaign.
Debenhams is expected to hold chemistry meetings with agencies at the beginning of next month about its UK advertising account, currently held by J Walter Thompson London.