When an organization decides on the level of flexibility in handling business process instances, it needs to impose this level in operational practice. The way of imposing a given level of flexibility depends on the means employed for controlling business processes. When a Business Process Support (BPS) system is used, the flexibility limits can be incorporated in it. The paper discusses how a given level of flexibility can be imposed by a BPS system built based on the state oriented view on business processes. This is done by combining different kinds of rules of planning: obligations, prohibitions, recommendations, and negative recommendations. Changing the status of a rule from obligation to recommendation, or from prohibition to negative recommendation gives more flexibility, and vice versa. The discussion is illustrated with the help of a simplified example already implemented in a BPS system called Probis.