Summary: In [Port. Math. 45, No. 3, 295-316 (1988; Zbl 0664.46042) and Note Mat. 7, 151-158 (1987; Zbl 0682.46027)], we introduced a distribution product, invariant under the action of compact Lie groups of linear transformations. This product has application to non-relativistic physics. Here, we present a general version of the product, invariant under various groups, including the Lorentz group.