In a letter to Assistant Attorney General Thomas Barnett, the Association of National Advertisers (ANA) in the US announced that it does not support the proposed online advertising venture between Yahoo! and Google, reported the European Journalism Centre (EJC) on Monday.

The deal might control 90 percent of the search inventory and might “diminish competition, increase concentration of market power, limit choices currently available and potentially raise prices to advertisers for high quality, affordable search advertising,” the letter claimed.

According to the EJC, Yahoo teamed up with Google in June to “shore up its advertising business” and to “ward off pressure to merge from Microsoft.”

Google and Yahoo said that they were not obliged to obtain a regulatory approval prior to implementing the deal, but had “voluntarily” postponed it for more than three months so as to allow anti-trust regulators to look over the venture.

The “non-exclusive” deal takes into account only the North American market and would let Google provide Yahoo with advertising services to be featured beside Yahoo searches. Yahoo has the second most popular search engine, wrote the EJC.

Google and Yahoo executives defend the deal, mentioning that instead they would compete in other spheres.