In diploid random mating populations with constant viability selection, genetic modifiers of recombination, introduced near equilibria that exhibit genetic association, invade if they reduce recombination. In this study we combine ecological and standard populations genetics in a haploid multilocus model that includes density-dependent regulation of population size and weak density-dependent differential selection among the multilocus genotypes. An allele that affects recombination among the genes contributing to the ecological selection, introduced near a stable equilibrium of the ecological-genetic system, invades if it reduces a weighted average of the recombination rates among pairs of loci under selection. This generalizes the Reduction Principle for the evolution of recombination (M. W. Feldman and U. Liberman, Proc. Nat. Acad. Sci. USA 83, 4824-4827, 1986; L. A. Zhivotovsky, W. M. Feldman, and F. B. Christiansen, Theor. Popul. Biol. 44, 225-245, 1993). It is also shown that the stronger the extent of density-dependence, the weaker the selection for reduced recombination.