A primer coating is provided for use on polymeric substrates to enhance adhesion of liquid toner to the substrates for printing in an electrophotographic printing device. The primer coating is water-based and includes a dispersion of a copolymer of ethylene and acrylic or methacrylic acid, and a compatible adhesion enhancer selected from an aliphatic polyurethane dispersion, a hydrogenated hydrocarbon rosin or rosin ester dispersion, and an amorphous acrylic polymer dispersion. The coating may also include additives such as wetting agents, antiblocking agents, matting agents, and waxes. The primer coating may be applied to a variety of polymeric substrates including polypropylene, biaxially oriented polpypropylene, polyethylene terephthalate, and polyvinyl chloride.