As speculated, the Department of Justice (DOJ) has finally filed a civil antitrust lawsuit in an attempt to block the merger between Halliburton Company HAL and Baker Hughes.Let us examine the primary reasons that led DOJ to block a merger valued at as much as $35 billion. Halliburton and Baker Hughes are the second and third largest oilfield services players in the world in terms of market capitalization. According to the justice department, if the two leading players merge, there will be plenty of opportunities for the combined company to take unfair advantage of the oilfield services market. The primary threats to the market include elimination of competition and increasing prices. The merger might also impede the innovations in the industry. As disclosed by DOJ, Halliburton is not willing to sell sufficient assets to clear regulatory activities. The justice department added that if Halliburton and Baker Hughes merge, the combined firm might eradicate competition for 23 services or products. However, both Halliburton and Baker Hughes believe that the merger will not give them unfair advantages. Rather, the merged entity should be able to serve clients with more efficient products and services. The cost of the products will also go down according to the companies.Investors should know that if the merger somehow gets completed, there will be two major players in the oilfield services industry. One will be the combined Halliburton and Baker Hughes and the other will be Schlumberger Limited SLB, the largest oilfield service player.Houston, TX-based Halliburton, an oilfield service provider, currently carries a Zacks Rank #5 (Strong Sell), implying that it will significantly underperform the broader U.S. equity market over the next one to three months.However, better-ranked stocks in the energy sector are Antero Resources Corporation AR and Vanguard Natural Resources LLC VNR. Both stocks sport a Zacks Rank #1 (Strong Buy).Want the latest recommendations from Zacks Investment Research? Today, you can download 7 Best Stocks for the Next 30 Days. Click to get this free report >>Want the latest recommendations from Zacks Investment Research? Today, you can download 7 Best Stocks for the Next 30 Days. Click to get this free report SCHLUMBERGER LT (SLB): Free Stock Analysis Report HALLIBURTON CO (HAL): Free Stock Analysis Report VANGUARD NATURL (VNR): Free Stock Analysis Report ANTERO RESOURCE (AR): Free Stock Analysis Report To read this article on Zacks.com click here. Zacks Investment Research