Microsoft and Expedia are among the companies raising preliminary concerns about Google's proposed acquisition of ITA Software, worried that the purchase of the top flight-information software company could give the search giant an unfair advantage, according to a Wall Street Journal report.

According to the newspaper, the comments were made in discussions with U.S. Justice Department investigators looking into the deal. The report says the broader inquiry is focusing on two areas -- whether rivals would still have access to ITA's data, and whether Google would unfairly favor its own travel services on search results pages.

Microsoft, Expedia and Kayak are listed as expressing concerns about the deal. The report says the investigation is still at an early stage, and it cites other competitors as supporting the deal.

A Google-ITA deal would put Microsoft in a somewhat awkward position, because its Bing Travel search engine uses Massachusetts-based ITA's search and pricing system. Google has said it will honor ITA's existing agreements, but Microsoft might be reluctant to rely on its rival for a core technology.

Expedia's technology could be another option for Microsoft to consider. The Bellevue company, which was spun off from Microsoft in 1999, offers its Best Fare Search as an alternative to ITA's airfare search and pricing technology. Best Fare Search has primarily been used for Expedia's own sites in recent years, but it has emerged a potential competitor to ITA for others in light of the Google acquisition plan.

In a recent blog post, Google cited technologies from Expedia and Worldspan as evidence that the online travel market would remain competitive even after the completion of the ITA acquisition.