It is not ethical for a company to require an employee to work overtime without compensation. This is not only unfair to the employee, but it is also a violation of labor laws in many countries.
Your colleague may want to consider speaking with their supervisor or human resources representative to discuss the situation and clarify the company's policy on overtime pay. If the issue is not resolved, your colleague may need to consider filing a complaint with the appropriate government agency or seeking legal advice.
Ultimately, the decision to resign from a job is a personal one and should be based on a variety of factors, including job satisfaction, career goals, and financial stability. If your colleague feels that the company is not treating them fairly, they may need to weigh the benefits and risks of staying in the job versus leaving and pursuing other opportunities.