Should there be drug testing for public assistance?

My dad is a truck driver and brought this question to me. His point is that he has to pay for his commercial driver’s license, be accountable for all state laws, and is subject to random drug testing. Not a problem, but he objects to spending his obligatory taxes on support programs if the recipients aren’t required to adhere to the same standards that he has to meet to earn his living.
I don’t know what to think about this. I am pretty liberal about social programs in general but this made me ponder.
What do you think? If public assistance programs are sponsored by the money of people whose jobs require drug-free test results, should the beneficiaries be subject to the same standards?