A top German regulator on June 28 raised the bar for the planned $30 billion merger of Deutsche Börse and London Stock Exchange Group, saying the headquarters of a combined exchange would have to be moved away from London.

His statement is the strongest call yet for altering the structure of the planned merger following the UK's vote to leave the European Union. German politicians and Germany's largest association of small investors have called on Deutsche Börse's top management around chief executive Carsten Kengeter to rework plans so the merged companies' new headquarters wouldn't be in London.