The study of extremal properties of the spectrum often involves restricting the metrics under consideration. Motivated by the work of Abreu and Freitas in the case of the sphere S 2 endowed with S 1 -invariant metrics, we consider the subsequence λ G k of the spectrum of a Riemannian manifold M which corresponds to metrics and functions invariant under the action of a compact Lie group G. If G has dimension at least 1, we show that the functional λ G k admits no extremal metric under volume-preserving G-invariant deformations. If, moreover, M has dimension at least three, then the functional λ G k is unbounded when restricted to any conformal class of G-invariant metrics of fixed volume. As a special case of this, we can consider the standard O(n)-action on S n ; however, if we also require the metric to be induced by an embedding of S n in R n+1 , we get an optimal upper bound on λ G k .