It comes as no surprise that Google is under the microscope of federal justice officials who are more closely reviewing the tech giant’s potential $12.5 billion acquisition of cellphone maker Motorola Mobility.

According to a filing with the U.S. Securities and Exchange Commission, Motorola Mobility Holdings and Google received a request for “additional information and documentary material” from the Antitrust Division of U.S. Department of Justice regarding the proposed merger between the companies.

“The companies intend to cooperate fully and respond expeditiously to the DOJ,” the SEC report said. The transaction is currently expected to close by the end of 2011 or in early 2012, according to the Sept. 28 SEC filing.

The Associated Press reported this week the U.S. Justice Department is “taking a closer look” at Google's proposed acquisition of Motorola Mobility, “raising the hurdle that must be cleared before the deal can be completed,” the report said.

Set to be Google’s biggest acquisition in the last decade, antitrust experts expect regulators to sign off on the Motorola Mobility deal too because there will still be plenty of other mobile phone manufacturers competing in the market, the AP said.

Officials with the Mountain View, Calif.-based company expressed confidence that the Justice Department will view in its favor.

“We're confident that the DOJ will conclude that the rapidly growing mobile ecosystem will remain highly competitive after this (Motorola) deal closes,” Dennis Woodside, a Google senior vice president overseeing the Motorola acquisition, wrote in a Sept. 28 blog post, according to the AP.

Because of Google’s powerful status, the U.S. Justice Department has closely scrutinized the company’s major acquisitions. For example, in April 2011, the Department of Justice ruled that for Google to proceed with its acquisition of ITA Software Inc., Google would have to develop and license travel software, to establish internal firewall procedures and to continue software research and development.

Last month, Google reached a deal to buy Motorola Mobility for about $12.5 billion, or $40 a share – a premium of more than 60 percent to Motorola’s closing price of $24.47, TechZone 360 reported.

If the deal falls through, Motorola will still make out: Google promised to pay Motorola Mobility $2.5 billion if it isn't completed, the AP said.