ask for advice

I work for a small company with 12 people. I am assistant manager and rank second at company. one day when I asked one of our staff for estimated time to finish a project (I estimated about two to three weeks) and he got angry and said i could not give you and I did not know how long it took, and he refused to give me a even guess. another time when I asked him to clean my office (he is our maintenance guy) he said that's not in his job description and he refused again. I want to give him a warning and tell him that the consequency is serious. What is the better way to tell him this is seriour issue? Should I talk to him alone? or should I ask GM to join me to talk to him?  He was hired by GM. Many thanks!!!