BRUSSELS: The World Federation of Advertisers has written to the European Commission urging it "closely examines" Google's planned $3.1 billion (€2.15bn; £1.51bn) takeover of DoubleClick.
The Brussels-headquartered WFA, a network of fifty-five national associations representing advertiser-interests, operates on five continents and represents more than forty of the world's top 100 marketers.
The letter expresses concern at the deal's potential to erode competition in online advertising.
Nor is the WFA's unease confined to Google. It also cites Microsoft's $6bn takover of aQuantive and WPP' Group's purchase of RealMedia.
In his letter, WFA managing director Stephan Loerke tells the EC: "Internet advertisers have benefited from innovation generated, in part, by intense competition. Global advertisers are keen to see this competitive marketplace maintained.
"It is hard to tell within such a rapidly changing marketplace what impact these proposed developments might have."
Loerke's members, who between them account for around 90% of global marketing spend, are concerned at the increasing concentration of advertising sales power in the hands of a diminishing number of outlets.
Google, however, insists that there are no real competition issues as DoubleClick's business model is different from its own.
But that's an argument unlikely to cut much ice with WFA members, whose collective corporate antenna are famously cost-sensitive.
Data sourced from MediaGuardian.co.uk; additional content by WARC staff