If a finite group of orientation-preserving diffeomorphisms of the 3-dimensional torus leaves invariant an oriented, closed, embedded surface of genus g > 1 and preserves the orientation of the surface, then its order is bounded from above by 12(g − 1). In the present paper we classify (up to conjugation) all such group actions and surfaces for which the maximal possible order 12(g − 1) is achieved, and note that the unknotted surfaces can be realized by equivariant minimal surfaces in a 3-torus.