Legal Question in Business Law in California

Only if the agreement was for each individual. If they say they will pay a married couple then they are only obligated to pay the "couple."

I agee with Mr. Natoli as far as his answer goes, but that illustrates the problem with your question. It is too vague and lacking details to answer. What does the employment agreement or per diem policy say exactly is the first question, as his answer implies. Are both members of the couple employed by the comany, or is the spouse a non-employee dependent traveling with the employee spouse? Is the employer a government contractor or otherwise subject to state, or federal per diem rules? The answer to this kind of issue depends entirely on the specific facts, which you have not provided.