  We study a unification of gravity with Yang-Mills fields based on a simple
extension of the Plebanski action to a Lie group G which contains the local
lorentz group. The Coleman-Mandula theorem is avoided because the theory has no
global spacetime symmetry. This may be applied to Lisi's proposal of an E8
unified theory, giving a fully E8 invariant action. The extended form of the
Plebanski action suggests a new class of spin foam models.
