It is very rare case for a supervisor not to write a reccommendation letter. This can only happen if the student has breached some form of committment to him or the student is a real problem. He is not a good supervisor if he is hesitent to furnish a rec letter. I would be more than happy to write a good letter to my own student if he is in very good standing. If you are in a degree program in the US and have some problem with any faculty member in the department, I have seen many aborting the program.