The influence of converse piezoelectric effect on the electro-optic coefficient of single domain relaxor-based 0.93Pb(Zn(1/3)Nb(2/3))O(3)-0.07PbTiO(3) (PZN-0.07PT) has been quantified under ambient conditions. It was found that the large piezoelectric constants d(31) and d(33) have significant influence to the half-wave voltage of electro-optic modulators. For single domain PZN-0.07PT crystal, Vπ13T is reduced by a factor of 8 and Vπ13L can be decreased by more than an order of magnitude due to the large piezoelectric effect. Compared to commonly used electro-optic crystal LiNbO(3) and BaTiO(3), PZN-xPT single crystal is much superior for optic phase modulation applications because they have much higher linear electro-optic coefficients and much lower half-wave voltage when piezoelectric strain influence is considered.