Is there a labor law that says something about overtime law/overtime pay? If an employee worked for 10 hours, is it compulsory for the employer to pay him for overtime hours worked?

Yes, any work rendered beyond the regular 8-hour period is considered overtime.

Thank you for your reply. I just have one more question.

There are employers who aren't paying for overtime worked. Is there a law that protects employees from employers like them? If so, what are the actions that may be done?

First of all if the employer DOES NOT prohibit the employee to work overtime then overtime is allowed, if the owner does not pay overtime the law applicable is Art. 87 of the Labor Code, inform the employee and if he refuses you can file an action to, if I'm not mistaken, to the National Wages and Productivity Commission.

what is the rule if the overtime work render during night time, let us say 12 midnight?

why is that the agrarian reform law was included as social legislation?