We consider a class of Riesz transforms $R_V^a$ related to the Schrödinger operator $L = -\frac{1}{2}\Delta + V$ with $V$ being a non-negative potential. We will focus on $L^\infty$ boundedness of $R_V^a$ and give a specific integral condition on $V$ which provides the boundedness. We will also show that potentials with power or exponential growth satisfy this condition.