I refused to extend twice. Both times, as per the FOM, I included the duty pilot in the discussion and never heard from the CPO. Recently, I flew with an FO who refused an extension, with full support from me. He was given a domicile layover, and I picked him up the next day to resume the balance of the trip. He said, the CPO office called him to gather some facts, but didn't give him any grief. Also mentioned to him, if you call the DP with the facts, you shouldn't get a call from the CPO unless they need further info.