You can try to either talk to them or leave a note and explain the issue to see how they respond before worrying about a feud.
If the dog is barking during the day there is not much you can do about it.
If the dog is barking during the hours of 10pm – 7am weekdays or 9am weekends then you can log a noise complaint and have animal control come talk to the neighbor for you. Keep track of the times and dates in a log and provide it to them.
If you believe the dog is barking due to neglect or abuse, like being left outside during a heatwave, you can call animal control and they will go to the neighbors and talk to them for you also.
It takes about 2-3 follow up complaints for them to then start being fined, but if they do not have a dog license, their rabies shots up to date and proof of all that when animal control shows up, then they could also be fined for both of those things as well.