Since the Duke of Saxony was considered one of the prince-electors electing a new Holy Roman Emperor , there was an argument between the lines of Lauenburg and Wittenberg about who should cast Saxony 's vote . Since the Duke of Saxony was considered one of the prince-electors electing a new Holy Roman Emperor , conflict arose between the lines of Lauenburg and Wittenberg over the issue of who should cast Saxony 's vote .