Seven states said they would join the U.S. Justice Department's antitrust suit to bar the $39 billion takeover of T-Mobile USA by AT&T.
The move comes only five days before U.S. District Court Judge Ellen Huvelle scheduled a first hearing in Washington, D.C.
The attorneys general of these states joined the lawsuit: California, New York, Illinois, Pennsylvania, Massachusetts, Ohio and Washington.
The Justice Department added the states to its lawsuit, noting that they had helped in its investigation. The lawsuit charges that by acquiring T-Mobile, AT&T would become the No. 1 U.S. wireless provider and stifle competition.
AT&T, based in Dallas, Texas, has filed counterclaims alleging the suit is misguided as has T-Mobile, based in Bellevue, Wash. T-Mobile is owned by Deutsche Telekom. Currently AT&T is No. 2 and T-Mobile is No. 4 in customers.
Verizon Communications of New York is No. 1. Its lawyers have filed briefs supporting the Justice Department's suit.
Judge Huvelle, in setting the hearing, also urged all parties to come before her to see if they can settle, a customary response in a federal antitrust case. An earlier case against AT&T was brought in 1946 and did not end until more than 40 years later, after the company was ultimately broken up.
AT&T shares rose 1.3 percent to $28.92 in late Friday trading.