We have calculated electron impact excitation cross sections between most of the low metastable levels of the 3d6 configuration in Fe III and of the 3d3 configuration in Fe VI have also been computed. The statistical equilibrium equations have been solved for a range of electron temperatures and electron densities, and the resulting level populations used to calculate emissivities for the forbidden lines of Fe III and Fe VI. Comparisons with observed line intensities and abundance determinations in planetary nebulae are in progress. (Paper submitted to The Astrophysical Journal.)