Why did IB launch it? IB: Please be advised that the previously announced reduction of the Stacking Limit (the number of orders allowed per contract, per side) to 15, will become effective Monday, March 2, 2009. Outstanding GTC orders that exceed this limit will not be subject to cancellation; however, any modifications to a pre-existing GTC order in this scenario will be rejected, while the original order will remain open. Any new order exceeding this limit will be rejected. There are no information on IBs website at the moment.