This paper deals with the problem of multibeam satellite precoding design under spectrum sharing constraints. These regulation restrictions allow the coexistence with other wireless services such as terrestrial mm-wave wireless local loop systems. This work focuses on the case where the satellite operator can use a certain frequency band whenever the signal power strength is limited in the coverage area. The precoding design is optimized considering this restriction by means of formulating a robust optimization. Numerical results sh ow the trade-off between the achievable rates of the satellite segment and the regulation violation outage