  In this Letter, we show that switching between repulsive and attractive
Casimir forces by means of external tunable parameters could be realized with
two topological insulator plates. We find two regimes where a repulsive
(attractive) force is found at small (large) distances between the plates,
canceling out at a critical distance. For a frequency range where the effective
electromagnetic action is valid, this distance appears at length scales
corresponding to $1-\epsilon(\omega) (2/\pi)\alpha\theta$.
