In yet another lawsuit against AT&T and T-Mobile, Sprint filed Tuesday its own in an attempt to block AT&T from acquiring T-Mobile.

The suit was filed in a U.S. District Court in Washington, D.C., where the Justice Department last week also sued AT&T and T-Mobile, a unit of Deutsche Telekom AG, saying their partnership would substantially lessen competition, Bloomberg reported.

Sprint Nextel Corp, the No. 3 wireless carrier in the U.S., also believes the merger could harm consumers and stifle competition. AT&T has a $39 billion bid to buy T-Mobile, which Sprint says would only strengthen AT&T, the second-largest carrier.

Sprint opposes AT&T's proposed takeover of T-Mobile, said Susan Z. Haller, Sprint's vice president of litigation, in a statement. With today's legal action, we are continuing that advocacy on behalf of consumers and competition, and expect to contribute our expertise and resources in proving that the proposed transaction is illegal.

With today's legal action, we are continuing that advocacy on behalf of consumers and competition, and expect to contribute our expertise and resources in proving that the proposed transaction is illegal, Haller said.

Both suits have been assigned to Judge Ellen Segal Huvelle. But The New York Times' Dealbook indicated more legal action might be on its way.

It is the first of a potential string of lawsuits aimed at stopping the blockbuster telecommunications merger, thought it would most likely be subordinate to the Obama administration's case, said Dealbook.

But the government's lawsuit seems to have taken the two phone carriers by surprise.

We have met repeatedly with the Department of Justice and there was no indication from the DOJ that this action was being contemplated, said AT&T's general counsel Wayne Watts, adding that it would fight the lawsuit. Deutsche Telekom said it would, too.

AT&T maintains the merger will allow it to better serve customers and expand its wireless network.