AdAge reports that MillerCoors pressured IPG after learning that Deutsch was working on ads designed to attack the authenticity of its brands.
MillerCoors is the US joint venture between Canada's Molson Coors and South Africa's SAB Miller. Interpublic agency DraftFCB handles all media planning for MillerCoors as well as creative on its two biggest brands, Coors and Miller.
Deutsch's ads for Anheuser-Busch have not been aired, but one was intended to highlight the fact that Coors and Miller are brewed at the same breweries.
It is unclear whether the ads will ever be used by Anheuser-Busch, which was acquired by Stella Artois owner InBev last year.
AdAge remarks that prior to their joint venture, Miller and Coors would not have had the clout to force Interpublic to part company with their rival.
Meanwhile, UK agencies have cause to feel aggrieved by Budweiser, which has asked participants in its ongoing £5m advertising pitch to sign over their intellectual property rights.