(Updates with U.S. filing amended complaint in first paragraph and comment from AT&T from fourth paragraph.)

Sept. 30 (Bloomberg) -- The U.S. Justice Department amended its lawsuit seeking to block AT&T Inc.’s $39 billion takeover of T-Mobile USA Inc., allowing Puerto Rico to join the case.

The government filed its amended complaint in federal court in Washington today. The Commonwealth of Puerto Rico is the eighth jurisdiction to sign on to the government’s Aug. 31 complaint, following seven states that joined Sept. 17.

The government’s antitrust suit claims that the merger, which would make Dallas-based AT&T the biggest wireless carrier in the U.S. and cut the number of national competitors to three from four, is anticompetitive and will hurt consumers.

“It is not unusual for state attorneys general to participate in DOJ merger review proceedings or court filings,” Michael Balmoris, an AT&T spokesman, said in an e-mail. “At the same time, we appreciate that multiple state attorneys general and hundreds of other local, state and federal officials are publicly supportive of our merger.”

AT&T continues to work on “parallel paths -- seeking a solution that addresses the DOJ’s concerns while simultaneously preparing for trial,” Balmoris said. The company remains “confident” it will “reach a successful solution,” he said.

The case is U.S. v. AT&T Inc., 11-cv-01560, U.S. District Court, District of Columbia (Washington).

--Editors: Fred Strasser, Stephen Farr

To contact the reporter on this story: Sara Forden in Washington at sforden@bloomberg.net

To contact the editor responsible for this story: Michael Hytha at mhytha@bloomberg.net