Although conservation and development are two facets of sustainability, they are often placed in contradictory positions. In this context, planning systems are able to respond to investment pressure, especially in countries with underdeveloped institutional solutions for this purpose, and are consequently characterized by a shifting relationship between spatial planning and environmental protection. Although these issues have been relatively well conceptualized, the literature still lacks more in-depth analyses of selected case studies. In order to fill the gap, this study aimed to identify potential ways to protect the environment and natural values in urban areas from investment pressures in countries with less developed planning systems, based on a comparative Polish-Romanian perspective. The method consisted of comparing the national legal frameworks for environmental protection and spatial development and analyzing in detail two case studies from each country. The findings indicate that national protection is required in both countries to ensure the effective protection of natural areas situated within city administrative limits that provide important ecosystem services. Moreover, the results reveal the need for more research on similar areas using multi-scale interdisciplinary approaches and reviewing planning theory with respect to its efficiency in protecting nature.