I would suggest that there are two tiers of work on Sunday. The first are those whose work is necessary for the society to function, 911 operators, fire fighters, etc… If they work on Sunday then it is ok. If they don’t go to mass because of their work then that is ok also. There is a second tier where the people work so that society can function in a comfortable manner, waitresses, cooks, gasoline station workers. They can work on Sunday so that people taking the day off on Sunday can be comfortable. However I think that they should arrange their day in such a way that they can get to Sunday mass.