The study aimed to reduce microbial contamination of sliced Kasar cheese. Oregano oil (OEO), garlic oil (GEO), nisin (NIS), and natamycin (NAT) containing whey protein isolate (WPI) films were used as layers onto Kasar cheese slices inoculated with Escherichia coli 0157:H7, Salmonella Enteritidis, Listeria monocytogenes, Staphylococcus aureus, and Penicillium spp. The microbial inactivation was determined during 15 days of storage. Kasar cheese inoculated with E. coli 0157:H7 layered with WPI-OEO film showed 1.48 log reduction, whereas the same film reduced S. aureus counts by 2.15 log when compared to control samples after 24 h. WPI films containing essential oils or NIS showed similar microbial inactivation pattern for S. Enteritidis. NIS containing WPI film had the highest microbial inactivation against L. monocytogenes, while NAT containing WPI films had the highest reduction against Penicillium spp. Application of WPI films containing plant essential oils on sliced Kasar cheese provided significant microbial reductions during storage.