Praise be to Allah.
Fasting Ramadan is obligatory for every Muslim who is an adult, of sound mind, not travelling and in good health. If he is sick or is travelling, it is permissible for him not to fast, because Allah, may He be exalted, says (interpretation of the meaning):
O you who believe! Observing As-Sawm (the fasting) is prescribed for you as it was prescribed for those before you, that you may become Al-Muttaqoon (the pious).
(Observing Sawm (fasts)) for a fixed number of days, but if any of you is ill or on a journey, the same number (should be made up) from other days
Based on that, if your work means that you have to travel in the bus to a place that is at the distance at which it becomes permissible to shorten the prayers, which is approximately eighty kilometers, then it is permissible for you not to fast whilst travelling, and you can make up the days when you did not fast after Ramadan is over, at times when it is easy to make them up, such as winter days.
If your work is inside the city limits, then you must fast and it is haraam to break the fast, unless you experience severe hardship on some day, in which case you may break the fast (by eating or drinking) whatever will ward off that hardship, then refrain from eating and drinking for the rest of that day, and make it up later on. That is because of the general meaning of the evidence which indicates that it is obligatory to protect oneself from death, to relieve hardship and not to take on more than one is able to bear.
It says in Sharh Muntaha al-Iraadaat, 1/478: If a person's work is (physically) hard and he will be harmed by not working, and he fears harm, he may break the fast and make it up later. That was stated by al-Aajurri. End quote.
In al-Mawsooah al-Fiqhiyyah (28/57) it says: The Hanafis say that in the case of the craftsman who needs to earn his living, such as a baker or harvester, If he knows that if he works at his craft it will cause him harm that makes it permissible for him to break the fast, it is haraam for him to break the fast before encountering hardship. End quote.
It says in Fataawa al-Lajnah ad-Daa'imah, 10/233: It is not permissible for one who is accountable to break the fast during the day in Ramadan just because he is working; but if he encounters severe hardship that forces him to break the fast during the day, then he may break the fast (by eating or drinking) whatever will ward off hardship, then he should refrain from eating and drinking until sunset and break the fast with the people, then make up that day on which he broke the fast. End quote.
If you know that you will not be able to combine fasting and work, then what you must do is look for another job, or take a leave of absence from work so that you will be able to perform this important pillar of Islam.
The Standing Committee for Issuing Fatwas was asked: What is the Islamic ruling on the case of workers who are doing physically hard work, especially during the summer months? I can give you the example of those who are working with smelting furnaces during the summer?
It is well-known in Islam that fasting the month of Ramadan is obligatory for everyone who is accountable and it is one of the pillars of Islam. Everyone who is accountable must strive to fast this month in fulfilment of what Allah has enjoined upon him, in the hope of earning His reward and fearing His punishment, without forgetting his share of this world and without preferring worldly matters to the Hereafter. If fulfilling what Allah has enjoined upon him of acts of worship conflicts with his worldly work, he has to try to find room for both so that he will be able to do them both. In the case given as an example in the question, he should make the night the time for his worldly work. If that is not possible, then he may take a leave of absence from his work during the month of Ramadan, even if that is without pay. If that is not possible, he should look for another job in which he will be able to combine both duties and his worldly concerns will not affect his striving for the Hereafter. There are many kinds of work and ways of earning money; it is not limited just to this kind of difficult work. The Muslim will never be without ways of earning a permissible income whilst at the same time being able to do the acts of worship that Allah has enjoined upon him, by Allah's leave.
And whosoever fears Allah and keeps his duty to Him, He will make a way for him to get out (from every difficulty).
3. And He will provide him from (sources) he never could imagine. And whosoever puts his trust in Allah, then He will suffice him. Verily, Allah will accomplish his purpose. Indeed Allah has set a measure for all things
If we assume that he cannot find any work other than what has been mentioned, which involves hardship, and he fears that he may be subjected to unfair laws or required to do things that prevent him from practising his religion and doing some of his religious duties, then let him flee for the sake of his religion from that land to another land where it will be easy for him to do what he needs to do for both his religious and worldly interests, and let him cooperate with the Muslims in righteousness and piety, for Allah's earth is vast. Allah, may He be exalted, says (interpretation of the meaning):
He who emigrates (from his home) in the Cause of Allah, will find on earth many dwelling places and plenty to live by
Say (O Muhammad SAW): O My slaves who believe (in the Oneness of Allah Islamic Monotheism), fear your Lord (Allah) and keep your duty to Him. Good is (the reward) for those who do good in this world, and Allah's earth is spacious (so if you cannot worship Allah at a place, then go to another)! Only those who are patient shall receive their rewards in full, without reckoning'
If he is not able to do any of the above and he is compelled to do something like that which is mentioned in the question of difficult work, he should fast until he feels that it is beginning to get too hard, then he may eat and drink enough to prevent that hardship, then refrain from eating and drinking (for the rest of that day). And he has to make up that fast on days when it is easy for him to fast. End quote.
Fataawa al-Lajnah ad-Daa'imah, 10/234
And Allah knows best.