As power consumption of the clock tree in modern VLSI designs tends to dominate, measures must be taken to keep it under control. This paper introduces an approach for reducing clock power based on clock gating. We present a methodology that, starting from an RTL description, automatically generates a set of constraints for driving the construction of the clock tree by the clock synthesis tool. The methodology has been fully integrated into an industry-strength design flow, based on Synopsys DesignCompiler (front-end) and Cadence Silicon Ensemble (back end). The power savings achieved on some industrial examples show that, when the size of the circuits is significant, savings on the power consumption of the clock tree are up to 75% larger than those achieved by applying traditional clock gating at the clock inputs of the RTL modules of the designs.