  In two-dimensional topological phases, quasiparticle excitations can carry
fractional symmetry quantum numbers. We generalize this notion of symmetry
fractionalization to three-dimensional topological phases, in particular to
loop excitations, and propose a partial classification for symmetry-enriched
$\mathbb{Z}_2$ toric code phase. We apply the results to the classification of
fermionic symmetry-protected topological phases in three dimensions.
