  We show that in the presence of large scale primordial hypermagnetic fields,
it is possible to generate an axial asymmetry for a first order electroweak
phase transition. This happens during the reflection and transmission of
fermions off the true vacuum bubbles, due to the chiral nature of the fermion
coupling with the background field in the symmetric phase. We derive and solve
the Dirac equation for such fermions and compute the reflection and
transmission coefficients for the case when these fermions move from the
symmetric to the symmetry broken phase. We also comment on the possible
implications of such axial charge segregation processes for baryon number
generation.
