Step 1: Understanding the Question:
The question asks us to identify the specific constitutional article that is referred to as the "charter of labor rights."
Step 2: Key Concepts and Approach:
Various Directive Principles of State Policy protect labor interests.
However, Article 39 contains multiple clauses that directly outline the socio-economic rights of workers (such as equal pay, livelihood, and health), earning it this title.
Step 3: Detailed Explanation:
• Article 39: This article contains fundamental principles of social and economic justice.
• Key Clauses for Labor:
- Article 39(a) directs the state to secure an adequate means of livelihood for all citizens.
- Article 39(d) mandates "equal pay for equal work" for both men and women.
- Article 39(e) protects the health and strength of workers from exploitation.
• Charter of Rights: Because these clauses address the core economic and physical vulnerabilities of laborers, Article 39 is widely regarded by legal scholars as the "charter of labor rights."
Step 4: Final Answer:
The provision referred to as the charter of labor rights is Article 39. Thus, Option D is correct.