Charge tennents for canceling service?

[Ramon Mota]

Can I charge a tenant for canceling a service request to fix something the day off or before I can cancel the work. This family has kids and I know fair housing seems to say that a worker can't enter without someone over 18 present. Now that this has happened more then 3 times I'm thinking of adding to the month to month agreement something that says canceling a service request 48 hours or less before the service time will make them have to pay a fee. something like $30.00 if it is me doing the service or what ever the workers company charges for the inconvenience. witch ever is higher. Is this legal to do? I want to add this to all of the units I'm managing because I normally let them choose from at least 2 days of the week.