The European Commission has blocked the proposed $9 billion merger between Deutsche Börse and NYSE Euronext. In effect, the decision has halted the plan by the German and U.S. groups to create the world’s largest equity and derivatives exchange.

The marriage of the two exchanges would have created the world’s largest platform for company listings and derivatives exchange.

According to senior European Union sources, the decision to reject the proposal was preceded by an unusually intense debate among the 27 commissioners. The decision to block the merger was fiercely challenged because it was considered a hindrance to the emergence of “European champions” in a global market.

“The merger between Deutsche Börse and NYSE Euronext would have led to a near-monopoly in European financial derivatives worldwide,” European Union’s antitrust chief, Joaquin Almunia argued. “These markets are at the heart of the financial system and it is crucial for the whole European economy that they remain competitive.”