Do I need polyurethane over latex paint before applying epoxy?

No. Latex and water-based paints don't need a polyurethane coat under the epoxy. Let the paint dry for at least 24 hours, then apply a seal coat of UltraClear Bar & Table Top Epoxy followed by the flood coat, just as you would on an unpainted surface. The epoxy seal coat is still required over paint; the polyurethane is not.

Oil-based polyurethane is only needed when the surface has oil-based paint or oil-based stain on it, because the epoxy will not bond to those finishes directly. In that case, apply 3 coats of oil-based poly before the epoxy (see 'Can you apply epoxy over paint?').

This applies to painted wood and painted concrete alike, and to pieces that will live outdoors, such as a latex-painted picnic table or sign. For anything kept outside, spray a coat of UV polyurethane over the epoxy after it has cured to help slow sun damage over time.