Google&39's proposed acquisition of travel software company ITA Software could face a DOJ review.

The U.S. Department of Justice is gearing up for a possible formal antitrust investigation into whether or not Google should be allowed to purchase travel software company ITA Software, according to a report.

Bloomberg reported today that DOJ lawyers have been asked to start getting ready for a possible challenge to the deal, which was first announced last summer. Such a challenge has seemed inevitable, as following completion of the deal Google would be in a position to control software that powers the reservations systems for many of the online travel booking agencies.

Google has said it plans to honor all existing agreements that ITA Software has signed with companies like Orbitz and Kayak, but a coalition of travel companies opposed to the deal isn't prepared to take Google at its word. The DOJ has been eyeing this one for several months, but work has taken on a degree of urgency because Google exercised its right to force the government to make a decision one way or another within 30 days of providing such notice, according to Bloomberg.

Such uncertainty involving large transactions could be a real problem for Google in 2011, if companies like Groupon that would automatically trigger federal review decide it's not worth doing business with Google and having to endure a six-month period of limbo.