 |  | Prospect of tougher antitrust regulation worries deal investors |  | WASHINGTON (Reuters) - The top U.S. antitrust regulator has sent a chilling message to dealmakers with his opposition to AT&T Inc buying Time Warner Inc : Companies do not have to be competitors for their merger to hurt competition, and there are no simple fixes to get such deals approved. | |  | |  |  | |  |  | Related Video | |  | |  | |  |  |  | Related News | |  | |  | |  |  |  |  |  | Make sense of the market with highlights of valuable financial information and reports along with compelling investment insights. Register Today |  | |  |  |  | Get a jump on the day with our early morning summary of key news developments for the US markets, as well as global market news. Register Today |  | |  | » » MORE NEWSLETTERS |  | |