As a measure to increase performance, improve safety and reduce environmental impact, the use of third-party logistics (TPL) solutions has increased in the construction industry. Other measures are inter-organizational collaborative methods and agreements between different actors. The purpose of this study is to explore how a TPL solution can affect inter-organizational relationships, specifically in the horizontal dimension. Findings are based on a case study of an urban development project with a TPL solution mandatory to use for all construction actors working side by side in parallel and sequential stages. The analysis is based on the industrial network approach, using the ARA-model for identifying and analyzing inter-organizational interactions among main contractors. The findings indicate that the contractors do collaborate with each other on both technical and organizational resources, as well as coordinate activities between each other, and that the TPL solution has a vital role in bringing them together and improves collaboration. This nuance the predominant view of the construction industry as being characterized by adversarial relationships and lack of inter-organizational collaboration. It also extends the knowledge of what a TPL solution can contribute with besides improved logistics.