A new technique is introduced for testing the validity of the spherical symmetry approximation of the Baade method for determining distances to supernovae.Lines with P Cygni profiles produced by resonance scattering in an expanding atmosphere with non-circular isophotes should show a linear polarization in excess of that in the continuum. Thus, spectropolarimetry offers a means of measuring the roundness of a supernova envelope and assessing the reliability of Baade method distances.So far, data has been obtained for two Type I supernovae. The data are discussed and interpreted in terms of a simple two-component atmosphere model for the polarization in P Cygni scattering profiles.