A quality management plan is a document that describes how the project team will ensure that the project deliverables meet the quality standards and expectations of the customer and other stakeholders1. Quality is not only about the final product, but also about the processes and activities that produce it2. A quality management plan defines the quality methodology, standards, criteria, activities, tools, resources, reporting, and corrective actions that will be applied throughout the project life cycle to achieve quality objectives3. A quality management plan is important because it helps the project manager and the project team to:
* Align the project scope with the customer requirements and needs
* Prevent or minimize defects, errors, and rework
* Enhance customer satisfaction and loyalty
* Improve team performance and collaboration
* Reduce project risks and costs
* Increase project value and benefits Therefore, the project manager should develop the quality management plan, as quality is as equally important as cost and schedule management. Quality is one of the key constraints of the project management triangle, along with scope, time, and cost4. Balancing these constraints is essential for delivering a successful project that meets the expectations of the customer and other stakeholders. Ignoring or compromising quality can have negative impacts on the project outcome, such as poor functionality, usability, reliability, or security of the software product, or low customer satisfaction, trust, or retention. The project manager should also communicate the importance of quality to the team member who complains about quality control, and explain how quality control activities, such as testing, inspection, or review, can help them identify and correct any issues or defects in their work, and ensure that they deliver a high-quality product that meets the customer's needs and expectations. References:
* The Quality Management Plan in Project Management | ProjectManager.com
* What is Quality Management? - Definition from WhatIs.com
* What is a Quality Management Plan (QMP) - AcqNotes
* Project Management Triangle - Time, Cost and Quality - Iron Triangle
* [Why Quality Matters in Software Development - DZone Agile]

The best course of action for the project manager in this situation is to review the stakeholder's communication requirements. This aligns with the principles of stakeholder engagement and communication management in project management. By reviewing the communication requirements, the project manager can ensure that the information needs of the stakeholder are being met without causing undue disruption to the team's work. This may involve adjusting the communication plan to provide the stakeholder with the necessary updates in a manner that is less intrusive to the team member's workflow.
: = The answer is verified by the principles found in the PMBOK Guide, which emphasizes the importance of managing stakeholder expectations through effective communication strategies1. Additionally, the Professional in Business Analysis Reference Materials supports the approach of tailoring communication to meet the needs of stakeholders2.

The project manager should follow the risk management plan that was developed during the planning phase of the project. The risk management plan should include a risk register that identifies the potential risks, their probability and impact, and the planned responses for each risk. Since the labor union contract negotiation was documented as a risk, the project manager should log the issue and execute the risk response plan that was prepared for this situation. This may involve implementing contingency plans, fallback plans, or workarounds to minimize the negative effects of the risk on the project objectives. The other options are not appropriate because they do not follow the risk management plan or they introduce new risks or changes to the project scope, schedule, or budget. References:
* A Guide to the Project Management Body of Knowledge (PMBOK Guide) - Sixth Edition, Chapter
11: Project Risk Management, pp. 397-441.
* PMP Examination Practice Questions: 400 Practice Questions and Answers to help you Pass, Question 400, p. 401.

The project manager should proactively engage with the stakeholders to address their dissatisfaction and work with them to find a solution. This is consistent with the stakeholder engagement plan, which defines the strategies and actions for managing stakeholder expectations and involvement. The project manager should not ignore the stakeholder issue, rely on the management team to intervene, or try to socialize with the stakeholders without addressing the root causes of the problem. References:
* PMP Exam Content Outline (2021), Domain III: Executing the Project, Task 8: Engage with stakeholders to meet expectations and foster relationships, p. 131
* A Guide to the Project Management Body of Knowledge (PMBOK Guide), Sixth Edition, Chapter 13:
Project Stakeholder Management, Section 13.3.1.1: Stakeholder Engagement Plan, p. 5182
* Professional in Business Analysis (PBA) Examination Content Outline (2018), Domain III: Analysis, Task 6: Manage Stakeholder Collaboration, p. 15