but as someone who worked in management my first response would be to ask my employee why they felt they couldn't discuss this with me first.
Two issues with this in Korea:
Subordinates are not supposed to challenge superiors, even when the superior is in the wrong. Read about Korean Air Flight 801 for a tragic example of this.
Complaining about your workload makes you seem "difficult" or "weak". Employees are expected to make sacrifices for the good of the company, even if it means accepting contract violations. This applies outside of the workplace too. If a husband complains to his family about how exhausted he is from working 60 hours per week, his wife may look down on him for lacking endurance. If a student complains about studying 12 hours per day, her parents may call her lazy.