In the context of the Bianchi universes, i.e., homogeneous but anisotropic cosmologies, we study the conditions to obtain vanishing shear that satisfy the cosmological principle. The anisotropic curvature has to be balanced by the anisotropic stresses of the non-perfect fluid that dominates the universe's energy density. Such a fluid has been considered to describe an $n$-form with or without potential. The scenario is successfully realised only for the free 0-form and 2-form cases, which are equivalent via Hodge duality.