Given a variety \({\mathcal{V}}\) with a constant 0 in its type and a lattice identity p ≤ q, we say that p ≤ q holds for congruences in \({\mathcal{V}}\) at 0 if the p-block of 0 is included in the q-block of 0 for all substitutions of congruences of \({\mathcal{V}}\) -algebras for the variables of p and q. Varieties that are congruence modular at 0 are characterized by a Mal’tsev condition. This result generalizes the classical characterization of congruence modularity by Day terms.