In this paper, we study the notion of an ordered semilattice congruence, and introduce the related equivalence relation n on po-semigroups. We study the least property of (ordered) semilattice congruences, and prove: 1. N is the least ordered semilattice congruence on po-semigroups (cf. [1]). 2. n is the least semilattice congruence on po-semigroups. 3. N is not the least semilattice congruence on po-semigroups in general. Thus, Ne give a complete solution to the problem posed by N. Kehayopulu in [1].