Your probation officer has a lot of cases to work. They can pretty much make sight guesses who their real problem clients are going to be. Those they can require all sorts of stuff from, including a monthly pee test. He/she has got you down to the monthly call in, but let them get the slightest wind of how you really feel about it all, or let you refuse and get all indignant about a spontaneous pee test they ask you to do some month, and you'll be back in the limelight. Same as if you get picked up again for another DUI or public drunkenness or jaywalking charge. The more trustworthy and proactive you seem to be, the easier they are going to be on you. But you let this quivering self-justification/bad attitude you've got going seep into even one conversation with this officer, and you'll be drug testing every month, and having to report somewhere to do it. And yes they can require it of you.