Opposition to the proposed Google and Yahoo ad sharing deal is mounting on both sides of the Atlantic.

The deal is already under investigation by authories in both the European Union and the US, and a coalition of independent organisations has also been formed to fight the deal.

But now individual politicians are wading in.

Reuters is reporting that a leading Republican lawmaker has contacted the US Justice Department to further urge them to "thoroughly investigate" the partnership.

Joe Barton, who is a Republican from Texas, took action after Yahoo failed to allay fears he and his staff had put to the web company.

"I am writing you to request that the Department of Justice thoroughly investigate issues of competition and privacy that Yahoo failed to address fully in responding to questions about the online search advertising partnership between Google and Yahoo", Barton wrote in a letter.

He went on to accuse Yahoo of obscuring rather than clarifying the motivations behind the deal calling Yahoo's response to his questions "a masterwork of crude redactions".

Both Yahoo and Google are not commenting but Hilary Schneider, executive vice-president of Yahoo US, told the BBC last month that the agreement was "fully within the guidelines of the law".