China's increasing regulatory influence over international mergers and acquisitions has helped to create the hottest new commodity in its legal industry: anti-trust lawyers. Six years ago, China did not even have a legal system for regulating the impact of M&A on competition. Today, its Ministry of Commerce is the biggest wildcard for dealmakers trying to get a major cross-border deal past anti-trust regulators. The ministry's decision last month to reject Danish shipping group A.P. Moller-Maersk's planned alliance with Swiss and French rivals came as a "big surprise" to Maersk Chief Executive Nils Smedegaard Anderson, whose team had been in close contact with the regulator until days earlier.