Regulators in the US are being urged to investigate any potential online advertising and search partnership between Google and Yahoo.
The call by a coalition of 16 American civil rights and rural advocacy bodies comes despite the fact no firm deal has actually been announced.
“We all suffer in such mega mergers,” Gary Flowers of the Black Leadership Forum told BBC News.
The justice department is examining a trial the companies did in April.
It has been widely reported that it is looking into the anti-trust implications of last month’s two-week test.
However, the department says it has no comment on the coalition’s demands because there is no definitive agreement between Yahoo and Google at the moment.
But reports say that the two companies are presently hammering out the intricacies of a future potential advertising and search agreement, and are sharing their plans with antitrust regulators.
At Google’s shareholder meeting on Thursday, Chairman Eric Schmidt said: “If there were a deal [with Yahoo], we would anticipate structuring the deal to address the anti-trust concerns that have been widely discussed.”