Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
Fasting is incumbent upon every Muslim, who is mature, sane, resident (not travelling), able, and free from what prevents fasting the month of Ramadan. What is meant by able here is a person who is not sick or very old and cannot fast. What is meant by free from what prevents fasting is for a woman not to be in menstruation or after childbirth (confinement period).
As for the people who manual labour they must fast and it is not permissible for them to break the fast except if they do not find enough food for their survival or those who depend upon them, such as their families. In this case, there is no harm for them to work, and if fasting is too hard for them, then they can break the fast and make it up in other days. But if they have enough (food), they must not subject themselves to hard work which will cause them to break the fast.
Ibn Hajar Al-Haithami (may Allah have mercy on him) said: If he is forced to earn daily bread for him and his dependents by breaking the fast, then it would be appropriate for him to break the fast, but not beyond necessity.
Allah knows best.