The U.S. Department of Justice has sued to block AT&T’s (T) planned $39 billion acquisition of T-Mobile from Germany’s Deutsche Telekom, on antitrust grounds. FCC Chairman Julius Genachowski also said today that the proposed tie-up raised “serious concerns” for his agency.

AT&T expressed surprise at the move, and said it would defend the merger in court.

AT&T shares are off more than 4.5% on the news, perhaps in part because AT&T would have to pay Deutsche Telekom $6 billion (including $3b in cash) were the deal to fail. Sprint (S) shares, on the other hand, are up more than 8% to $3.83 a piece. Verizon (VZ) is down 1.4%.

All of this comes just hours after AT&T announced that it would bring 5,000 call center jobs back to the U.S. after the T-Mobile acquisition closed. It also said that it would increase its U.S. infrastructure investment by more than $8  billion, which could create around 96,000 new U.S. jobs. The company did not, however, publicly discuss how many job losses could result from the merger, due to redundancies with T-Mobile.

That could be a pretty big bargaining chip with the jobs-hungry Obama Administration, and the timing perhaps indicates that AT&T knew what Justice had planned for today.

At a press conference, Acting Assistant Attorney General Sharis Pozen said: “We conducted dozens of interviews of customers and competitors, and we reviewed more than 1 million AT&T and T-Mobile documents.  The conclusion we reached was clear.  Any way you look at this transaction, it is anti-competitive. Our action today seeks to ensure that our nation enjoys the competitive wireless industry it deserves.”

Bank analysts are still scrambling to digest the news, but Wells Fargo’s Jennifer Fritzsche has already released an initial report. She says, in part: “If it is not approved, we would remind investors that while T likely would need more spectrum longer term (like VZ), it does have over 20 MHz of 700 MHz spectrum in the top 100 U.S. markets. We anticipate that T would pull back on its commitment to over 95%+ of the U.S. with LTE. But in no means do we believe T is a broken wireless story without T Mobile in hand.”

What follows is a copy of the DoJ complaint, filed in U.S. District Court in Washington:

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