(CHARLOTTE) --  Duke Energy is guaranteeing a $10 million line of credit for the 2012 Democratic National Convention.   The Charlotte Business Journal reports the massive credit line is being extended to guard against a shortfall. Among the uses of the money will be for retrofits within Time Warner Cable Arena, production costs and for transportation for delegates and media to an from the event.   However, the Republican National Committee is crying foul.   The GOP says the Democrats are using the credit line to get around a rule that limits cash contributions.   DNC officials say if the line is used and not repaid, Duke Energy shareholders will be on the hook for it.