Final answer:
The manager should first engage in an open dialogue and problem-solving with the employee to understand the tardiness and customer complaints, offering support before escalating to formal warnings or termination.
Step-by-step explanation:
When dealing with a restaurant employee in a nonunion environment who has issues with repeated tardiness and customer complaints, the manager's first step in the disciplinary process should be C. Open dialogue and problem-solving. This approach involves sitting down with the employee to discuss the issues at hand and seek to understand the reasons behind their behavior. It is essential to establish clear communication and provide support or resources that the employee may need to improve. If this does not resolve the issues, the manager may then move on to more formal disciplinary actions, such as an oral warning or a written warning, before considering termination as a last resort.