U.S. regulators are cobbling together a possible antitrust challenge to Google Inc.’s plans to purchase ITA Software, an airline ticketing software company, Bloomberg reported today.

Google’s pursuit of ITA Software, whose travel programs are used by companies including Orbitz Worldwide and Microsoft, began last summer. The proposed deal ruffled feathers among online travel sites that feared Google’s acquisition of ITA would prevent them from using the software company’s business-critical products and services.

According to the Bloomberg report, officials in the Justice Department’s antitrust division have requested prompt access to more information about the merger. Bloomberg also reported that Google invoked a provision of federal law that compels U.S. officials to decide within 30 days whether to challenge the deal.

Google’s planned acquisition of ITA Software is part of the tech giant’s ongoing shopping spree. Last August alone, Google purchased six companies, a single-month record for the company. And in 2010, Google purchased more than two dozen companies, compared to its previous annual record of 16 in 2007. Many of these acquisitions relate to social networking including SocialDeck, Angstro, Jambool and Slide.com.

In fact, Google’s acquisition pace is significantly greater – almost double – of the next most acquisitive tech company, IBM.  Google’s mix of acquisitions is quite varied combining larger acquisitions ($100 million plus) and also doing smaller talent acquisitions (the popularly coined “acqu-hire”), according to CB Insights.

Among Google’s latest acquisitions is Zetawire, a Canadian startup specializing in mobile payments. Little is known about Zetawire although Mashable reports that an analyst with 451 Group reveals that the fledgling company received a patent for “mobile banking, advertising, identity management, credit card and mobile coupon transaction processing.”