I work in the oilfield away from my home seven days a week. The company i work for most of the time works six days a week except on occation we work seven. They only pay per diem based on days worked not time away from home. On the days we dont work which is an occational sunday off should they have to pay per diem to help with our expences. By the way we have to pay rent weekly or monthly no matter if we work or not.
I really don't know about this as it is more of a legal question concerning time and wages rather than drilling technology but it may guide your actions if I recount what I have seen and what I have received for myself.
I am a consultant and therefore time and wage rules do not apply to me. This is also true for many salaried jobs that are considered exempt. The employers of non-contract hourly paid workers are subject to rules that cover overtime and per diem rates.
In my own case, my clients pay me a per diem or provide lodging and meals depending on our agreement and work area. Typically, on a land job that is within one days driving distance, they will pay per diem starting the day I arrive at the rig and it stops when I depart. This is customary regardless of how long I take to drive to work or return. They also don't pay waiting time unless it has been agreed to in our contract. Offshore and remote location jobs don't pay per diem as they provide housing.
Back in the day, when I was working as a "Roughneck" or "Service Hand", we were paid our hourly wages and paid all of our expenses ourselves. The crews generally pooled our money to share the cost of housing and sometimes even rented short term housing with a kitchen. During the same time period I also worked for companies that paid a generous, all-inclusive, per diem. Federal wage and hour laws were similar then as now.
This may mean that your employer really does not have to pay any per diem at all. I don't know this.
A lot of what your company must do, as opposed to can do, would depend upon your status. Are you a direct employee or an Independent Contractor, are you an exempt or non-exempt hourly or salaried employee?
The big companies such as B.J., Stallion, Nabors etc have very specific policies and their many lawyers make sure that they are in compliance and are usually willing to explain these policies. Obviously, you work for a smaller, possibly privately owned, company. This being so, you are also aware that if you question or demand too heavily someone will find an excuse to lay you off. What I would suggest is simply asking your immediate supervisor if you can talk to his boss about employee born expenses. When I was carrying these myself I kept records of them and deducted them on the federal tax return. There is a schedule to do this. Also, if you are having to drive a long distance to the work site you may be able to deduct the mileage if it does not fall under commuting rules. If you are classed as an Independent Contractor your per diem must be reported as income and all of your expenses are deductible.
Again, I can't give a specific answer to this legal question. There are volumes of federal work rules but also many ways companies can work around them. Work rules also vary from state to state. It may be that they don't legally have to pay you anything, I don't know. If you feel this burden reduces the value of your job to where it is below what you can earn by staying near your home, talk to your co-workers to see how they feel in order to possibly raise the issue with management.
While in collage, I worked one summer for a company that offered me a raise. On advice from my foreman I asked to receive increased per diem instead. This increased my deductions and reduced my income tax. Perhaps you could try that.