Answer:
Undue influence
Explanation:
Undue influence occur when a person uses is position to force or induce another person to do what he or she does not wish to do.
Justin father was taking advantage of Justin because he is his agent there by inducing Justin to give him fifty percent of his income because of the contract between them which Justin didn't wish to do but due to the condition given to him by his father he agreed to give him part of his income. This act by Juston father is called UNDUE INFLUENCE because Justice was induce to act otherwise against his wish and will.