Google and the U.S. government are headed for a legal showdown, but on different sides of the courtroom than one might expect.

Eric Goldman, a law professor with Santa Clara University who closely follows the tech industry, spotted a lawsuit filed by Google against the federal government claiming that the U.S. Department of the Interior did not properly evaluate Google Apps when choosing a new Web-based document system. Google alleges that because the Interior Department specified that the system needed to be part of Microsoft's Business Productivity Online Suite, Google Apps never had a chance despite repeated attempts by Google to explain the product.

"Significantly, the SOW (statement of work) and even certain terminology were closely aligned with Microsoft's product literature for its Exchange Online, SharePoint Online, and Office Communications Online applications. This was because the DOI had defined its needs and requirements around the Microsoft products," Google wrote in its complaint.

Government agencies generally have to follow a complicated process to purchase products or services from technology companies, and Google has increasingly sought to position itself as an alternative to Microsoft's office software in companies and governments.

And, of course, the federal government and Google are no strangers when it comes to legal maneuverings. The most current dispute involves Google's proposed acquisition of ITA Software, but the list stretches back several years.

Updated 4:25 p.m. PDT: Google issued the following statement on its lawsuit:

"Google is a proponent of open competition on the Internet and in the technology sector in general. Here, a fair and open process could save US taxpayers tens of millions of dollars and result in better services. We're asking the Department of Interior to allow for a true competition when selecting its technology providers."

A copy of the complaint follows below:

Google v US Complaint

Tom Krazit writes about the ever-expanding world of Google, as the most prominent company on the Internet defends its search juggernaut while expanding into nearly anything it thinks possible. He has previously written about Apple, the traditional PC industry, and chip companies. E-mail Tom.