  Using the Coulomb gauge formulation of QED we present a lattice QCD procedure
to calculate the $\pi^+\pi^+$ scattering phase shift including the effects of
the Coulomb potential which appears in this formulation. The approach described
here incorporates the effects of relativity and avoids finite-volume
corrections that vanish as a power of the volume in which the lattice
calculation is performed. This is the first step in developing a complete
lattice QCD calculation of the electromagnetic and isospin-breaking light-quark
mass contributions to $\varepsilon'$, the parameter describing direct CP
violating effects in $K_L\to\pi\pi$ decay.
