Launching the most significant challenge against the AT&T/T-Mobile merger to date, the U.S. Justice Department (DOJ) filed suit on Wednesday to block the $39 billion deal, arguing that the merger will remove a significant wireless market competitor (T-Mobile) that has the power to constrain prices industry-wide. Announced last March, the proposed union of AT&T and T-Mobile would combine the second- and fourth-largest national wireless operators to establish a market colossus that would easily leapfrog Verizon Wireless as the top wireless carrier in the U.S. In a complaint filed with the U.S. District Court in Washington, D.C., the DOJ charged that AT&T’s proposed takeover of T-Mobile would “substantially lessen competition for mobile wireless telecommunications services—resulting in higher prices, poorer quality services, fewer choices, and fewer innovative products.” While lauding T-Mobile as a market trendsetter that was the first U.S. carrier to adopt the Google Android operating platform, the complaint also states that T-Mobile “places important competitive pressure on its three larger rivals, particularly in terms of pricing” and that the elimination of T-Mobile as an independent rival against AT&T, Verizon Wireless and Sprint Nextel “would remove a significant competitive force from the market.” Although Deputy U.S. Attorney General James Cole told reporters on Wednesday that millions of mobile telephony consumers would be left with fewer choices as a result of the deal, Cole stressed that the “door is open” for AT&T to propose remedies that would address the DOJ’s concerns. Should the DOJ succeed in blocking the deal, AT&T would be required to pay T-Mobile a hefty break-up fee of $3 billion and also provide T-Mobile with spectrum access and roaming arrangements that are valued at an additional $3 billion. Promising to “vigorously contest this matter in court,” a spokesman for AT&T said company officials are “surprised and disappointed” and “plan to ask for an expedited hearing so the enormous benefits of this merger can be fully reviewed.”