Perceptions of and reactions to injustices are an integral component of human life. The proposed study aims to capture them, in the sense of the level of employees’ work engagement and job performance, in a situation. When employees simultaneously perceive (in)justices deriving from multiple sources. Data collection will run across six countries on a convenience sample of employees in non-managerial positions in various industries (i.e., insurance companies, call centres and banks). Polynomial regression analysis combined with response surface methodology will simultaneously capture main effects and interactions of justice sources on work engagement and performance.