Ukrainians in work camps during World War II?

My Grandparents are from Ukraine and I remember my father telling me they were put in working camps during the Holocaust. I can't understand this since we are not Jewish. Unfortunetly my father and both grandparents have ped away so I can't ask them directly. I tried to do some research but have not been able to come up with anything. Does anyone know why a Ukrainian Orthodox couple would be put in working camps during World War II?