  We examine the unitarity properties of spontaneously broken non-commutative
gauge theories. We find that the symmetry breaking mechanism in the
non-commutative Standard Model of Chaichian et al. leads to an unavoidable
violation of tree-level unitarity in gauge boson scattering at high energies.
We then study a variety of simplified spontaneously broken non-commutative
theories and isolate the source of this unitarity violation. Given the group
theoretic restrictions endemic to non-commutative model building, we conclude
that it is difficult to build a non-commutative Standard Model under the
Weyl-Moyal approach that preserves unitarity.
