In project management, especially when dealing with complex projects and unclear requirements, it is crucial to involve all stakeholders, including contractors, in regular communications. This ensures that everyone has a clear understanding of the project objectives, customer requirements, and can contribute to the solution design effectively. According to PMI's guidelines, collaboration and stakeholder engagement are key to project success. The PMBOK Guide emphasizes the importance of involving all team members in planning and decision-making processes to enhance buy-in and reduce resistance. Therefore, welcoming and involving the contractors as part of the project team is the best approach to address their concerns and ensure that the project benefits from their expertise and insights. : Project Management Institute. (2021). A Guide to the Project Management Body of Knowledge (PMBOK Guide) - Seventh Edition and Standards. Project Management Institute.