Officer Smith is patrolling a city park at night. He comes across a man and woman kissing in a parked car, and tells them that it is not legal to be in the park after dark and that they need to move along. Later, he comes across two men in a parked car. Instead of telling them to move on, Officer Smith writes a citation for the driver. By allowing his personal views to result in unequal treatment of members of the public, Officer Smith is in violation of his ___________________.