Computer software giant Microsoft has joined the ranks of companies opposing Google's proposed acquisition of ITA Software, which powers most of the online airfare search sites.

An organization called Fairsearch.org, formed by Expedia Inc., Farelogix Inc., KAYAK and Sabre Holdings was formed in October, and came out against the merger. The problem, Fairsearch says, is that once Google buys ITA it might eventually cut the company off from its users. Besides Microsoft, Foundem, a UK-based search engine that offers price comparisons and Level...com, a Paris-based online travel agency association have also said they will oppose the deal.

ITA provides the technology behind sites such as kayak.com and Orbitz. Google says it wants to buy the company for $700 million, but the Federal Trade Commission has to sign off on the transaction.

In addition to the travel-specific issue Fairsearch says is a problem, there is now concern that Google is already privileging its own companies in search results over competitors. In the latter case, Google's own travel search products would appear ahead of other companies.

Besides the formal members, Fairsearch.org has garnered support from Amadeus, a Miami-based company that provides software and hardware systems to the travel and tourism industry.

While we are still considering our involvement in any coalition effort, we share the concern that the proposed merger of Google and ITA Software could affect travelers around the world, said CEO David V. Jones, in a statement. The outcome of this debate is extremely important to both the future of the online travel industry and the Internet as a whole, and we urge regulators to carefully scrutinize the deal to ensure consumers are protected from potential harm.