This article discusses formalization processes in the context of urban conflict, focusing on the ways adversarial power relations dictate methods and outcomes of formalization. Based on analysis of the formalization of public transport in ethno-nationally contested Jerusalem, the article demonstrates the production of a mode of formalization, which the author terms sub-formalization. This mode is characterized by severe deviation from professional and administrative norms, both in methods and outcomes, and usually results in inferior solutions and irregular arrangements for challenging informality. In sub-formalization, modern rationality – which constructs planners’ professional authority – is eroded by powers from above and below. Therefore sub-formality represents a mutation of modern, rational, West-oriented planning, coming as a result of the encounter with informality and resistance in a way that blurs dichotomization between the formal and informal. In the context of an ongoing urban conflict, as in the case of East Jerusalem, sub-formality is also utilized by the state to maintain urban marginality and secure existing power hierarchies.