During planning, the project manager is told one activity cannot start until another department implements a required IT system. What should the project manager do?

The project manager should document the dependency in the project schedule. This is a fundamental planning activity that ensures all known constraints and relationships between activities are formally recorded. Documenting it allows for proper scheduling, resource allocation, and risk management. Fast-tracking is a schedule compression technique, not a primary response to a newly identified dependency, and might not be feasible or appropriate without further analysis. Performing integrated change control is premature; this is a planning activity, not yet a change request. Asking IT to prioritize the system is an action that might follow documentation and analysis, but the immediate and most appropriate step is to formally record the dependency.