Large-bandgap materials can support very high electric fields (>lMV/cm) without breaking down. The possibility then exists for an electron in a conduction band to become quasi-localized in Wannier-Stark states, a possibility that depends on the scattering rate being less than the Bloch oscillation frequency. If this condition is met the scattering rate itself is affected and the description of transport must be changed from the usual model in which the electron is assumed to be virtually free. Here, we examine the feasibility of obtaining this condition in GaN using a simple three-dimensional tight-binding model for the bandstructure and taking the dominant scattering mechanism to be the polar and non-polar interaction with optical phonons and short-wavelength acoustic phonons.