In a number of earlier religious Dispensations and in certain cultures the kissing of the hand of a religious figure or of a prominent person was expected as a mark of reverence and deference to such persons and as a token of submission to their authority. Bahá’u’lláh prohibits the kissing of hands and, in His Tablets, He also condemns such practices as prostrating oneself before another person and other forms of behaviour that abase one individual in relation to another.
Reference: Kitáb-i-Aqdas, Pg 254, Bahá’í World Centre, 1992 edition
Note: There are multiple instances of both Bahaullah and Abdul Baha going against this law and enjoying the fame and position of their followers coming and kissing their hands.
12 Principles of the Baha'i Faith 