There are certainly two ways to look at every business choice we make; 1) the legal boundaries governing such and 2) the ethical boundaries governing such.
There are plenty of legal boundaries that we all have to know about and ought to try to abide by. Some of the listers on this site have already mentioned the city ordinances that govern the work that we do. They tell us what days and hours we can work, what decibel noise level our equipment has to adhere to, what licensing, insurance, etc we might need to be in practice, etc, etc. Some local ordiances or state laws will specify ISA compliance in tree care methods (ie. no topping, what trees to plant where, etc). Other laws even go so far as to address neighbor conflict issues such as who can prune what limbs on their neighbor's tree if it hangs over on their property. And the list goes on and on...
Legal boundaries should be fairly easy for just about anyone in this industry to comply with. Not much room for personal interpretation when it's all spelled out in black and white.
Ethics is a bit trickier. While legally, you might be allowed within your area to operate chippers and chainsaws on a Sunday, ethically, you have to ask yourself if it's the right thing to do considering the customers you are serving. If you're a non-christian and your customer is a non-christian and most of the people in your service area are all non-christians, then I'm not going to tell you not to work on a Sunday. Afterall, in such a scenario, Sunday doesn't mean anything more to you, your customer or your service area residents than Saturday does. But, if by serving that one non-christian customer by working on Sunday offends 20 of his neighbors and area residents, then maybe you need to stop and ask yourself if you're doing the right thing.
Perhaps, it's not so much an ethical question as a business decision but I think everyone gets the point. Think of Sunday as a holiday that occurs 52 times a year for Christians. Working on Sunday is like working on a Christian holiday as some see it. It might sound rediculous to many of the folks on this site and that's your own opinion that you're entitled to but, the question asked in the original post was "is it ok to run saws on Sunday?" I don't believe the question was asking 'do any of you other service guys mind if I run my saws on Sunday'; rather, 'do you guys think my customers will mind?'
I think the answer will vary in each part of the country but just look at the attached statistics chart. You'll see that 76% of Americans identify themselves with Christianity. That means 3 out of 4 of your customers are Christians. That means that, while not all of the Christians might be upset by your idea of working on Sunday, there's still a pretty good chance that you're going to piss off the majority. Is it worth alienating many to please a few? Remember, it's not the 30-50 year-old guys who are your customers. It's the little old church ladies and nobody spreads information faster than little old church ladies! God help you if you make them mad...
