Advertisers have opposed the potential ad deal between Google and Yahoo in a letter sent to the US Department of Justice.
The deal, announced in June, would allow Google to display text ads on Yahoo, with Yahoo deciding when and how the ads display and taking a cut of revenue.
In its short announcement of the letter, the Association of National Advertisers stated the deal "will likely diminish competition, increase concentration of market power, limit choices currently available and potentially raise prices to advertisers for high quality, affordable search advertising".
The Wall Street Journal digs into the drama and history of the deal, which came about during Microsoft's attempt to buy all or part of Yahoo. The story notes that the ANA is a major trade group representing clients such as Procter & Gamble and General Motors Corp, but that some "large advertising agencies and midsize advertisers have endorsed the deal".
Also, BusinessWeek's Rob Hof writes that he thinks "it's hard to see harm" in the deal, and that he doesn't quite buy opposition arguments that the deal would necessarily result in higher ad prices.
As to whether the ANA letter will have any effect, the WSJ notes that the ANA opposed Google's purchase of DoubleClick as well, but that the FTC approved the deal anyways.