We consider the 3D Pauli operator with nonconstant magnetic field B of
constant direction, perturbed by a symmetric matrix-valued electric potential V
whose coefficients decay fast enough at infinity. We investigate the low-energy
asymptotics of the corresponding spectral shift function. As a corollary, for
generic negative V, we obtain a generalized Levinson formula, relating the
low-energy asymptotics of the eigenvalue counting function and of the
scattering phase of the perturbed operator.