1T-TaS2 is a 2D quantum material supporting charge density waves (CDWs) at room temperature. The strong correlations in this material make its electrical properties extremely sensitive to external stimuli such as an electrical bias and illumination. Recently, we demonstrated that the optical properties of this material also considerably change with electrical bias and light. With light, we showed that the CDW domains across layers stack differently and thus result in a unity-order change in the refractive index. Here, we demonstrate that an in-plane electrical bias also changes the CDW stacking in 1T-TaS2. However, the stacking change with electrical bias opposes that with illumination. Our experiments at room temperature suggest that an in-plane electrical bias sets the CDWs sliding and making way for the higher energy stacking configurations to switch to the ground-state stacking. The demonstration here sheds light on the origin of the giant electro-optical effect previously observed in 1T-TaS2 and paves the way for low-power MHz-fast electrically tunable optical devices.