Several online travel companies have teamed up to fight Google's proposed acquisition of ITA Software.
Expedia, Kayak, Sabre and Farelogix have formed an organization called FairSearch to lobby the Justice Department and Congress to block the deal on the grounds that it would allow Google to unfairly dominate the market.
Google agreed to acquire ITA in a $700 million deal earlier this year. The DoJ said it planned to investigate in July.
"Acquiring ITA will gove Google control over the search algorithm software that today powers most of Google's closest rivals in the travel vertical," says FairSearch.
"Combined, Google could use ITA to try and marginalize competitors in ways that raise prices for consumers and limit innovation - a pattern of behavior that fits Google's last acts."
For example, it says, Google could withhold licensing the software to companies that it considered a threat. It could also direct people using its search services away from its competitors.
The group claims that 82 percent of people already name Google as their preferred search provider for travel services, and that 30 percent of travel searches already begin with Google.
"This threatens to harm competition in the industry, limit innovation, expand Google's dominance in search overall, and could ultimately lead to fewer choices and higher travel prices for consumers," says the group. "The DoJ must challenge the deal in order to protect the interests of the largest segment of the internet economy."