Production planning is a scheduling process to acquire, utilize, and allocate production resources to specific production activities in the most efficient way, meeting customer expectations. Due to, e.g., climate crisis, customer expectations are changing shift to be more sustainably produced products. Therefore, decision-makers have to adjust economic production planning goals according to social and environmental aspects. However, driven by financial market expectations, most enterprises still consider the economic dimension more important than the other two. Especially the social dimension has been neglect in previous approaches for sustainable production planning. The paper presents a concept of a fuzzy inference model (FIM) to assess the social-sustainability of production programs using expert knowledge. The concept shows the formulation of the FIM using common methods and fuzzy operators from the fuzzy set theory. The FIM determines the sustainability potential to improve the production program. The concept was applied in a case study. For the case study, the FIM has been implemented in a simulation model of a job shop learning factory.