"It's a combination of the FTC and (Justice Department) being willing to litigate and the fact that companies are fighting back," Grosberg said. More recently, they have lost four attempts to block mergers in court, though they are appealing two of the cases. The Justice Department did not immediately respond to requests for comment. Break-up fees that acquirers agree to pay their targets if their deal gets shot down by antitrust regulators are also on the rise. Many companies facing merger challenges say they will fight on, emboldened by the four court losses of the Justice Department and FTC.

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