WASHINGTON, Aug. 31 (Xinhua) -- The Justice Department of the United States on Wednesday filed an antitrust lawsuit to block AT& T's acquisition of T-Mobile, Deputy Attorney General James M. Cole said at a press conference.

Cole said that four nationwide providers, including AT&T, T- Mobile, Sprint and Verizon, account for more than 90 percent of the mobile wireless connections in America, so "preserving competition among them is crucial."

A merger of AT&T and T-Mobile, however, would combine two of the four largest competitors in the marketplace, and would eliminate T-Mobile, an aggressive competitor, from the market, he said.

An At&T logo is seen atop a store in Beverly Hills, California August 31, 2011. The Obama administration on Wednesday fired a legal broadside to block AT&T Inc's 39 billion U.S. dollars acquisition of T-Mobile, launching its biggest challenge yet to a takeover and dealing the carrier a potentially costly blow

The combination of the two companies would also result in tens of millions of consumers facing higher prices, fewer choices and lower quality products for their mobile wireless services, he added.

"We are seeking to block this deal in order to maintain a vibrant and competitive marketplace that allows everyone to benefit from lower prices and better quality and innovative products."

AT&T is the second largest mobile phone service provider in the U.S.and T-Mobile is ranked the fourth largest. Since AT&T's proposed 39 billion U.S. dollars acquisition of T-Mobile was released in March, the deal has proved controversial, with increasing opposition from rivals, consumer advocates and organizations.