Using the Lorentz transformation, the Klein–Gordon and Dirac equations with moving potentials are reduced to one standard where the potential is time-independent. As application, the reflection and transmission coefficients are determined by considering the moving step with a constant velocity $v$. It has been found that $R \pm T = 1$ only at $x = vt$. The problem of massless (2+1) Dirac particle is also considerered.
