Abstract. We prove an extension of a celebrated equivariant bifurcation result of J. Smoller and A. Wasserman [20], in an abstract framework for geometric variational problems. With this purpose, we prove a slice theorem for continuous affine actions of a (finite-dimensional) Lie group on Banach manifolds. As an application, we discuss equivariant bifurcation of constant mean curvature hypersurfaces, providing a few concrete examples and counterexamples.