Labour Law

How far can labour law protect employees themselves??? One of my fren hav just resign her job coz her boss asked her to overtime after normal working hour but yet no extra ot can be claim... what happened actually??? I though once the employees commence 8hours working hours den the extra hours they work on is considered as overtime... but all of her collegues just work extra hours without any ot claim... cant believe that it happen in now... what use of the labour law??? can protect the employees fully or just a part only... I til wondering... I trust law can justify the truth and fair but smthg it does work as I though... haiz