When it comes to the legality of a dog barking the dog can legally bark every few minutes as often as it wants too or needs to bark.
But the dog cannot bark longer than 20 minutes consecutively in a row and if the dog is constantly barking and never or hardly ever shuts up or the barking continues through the night then it can become illegal for the dog to do so.
If your town has noise ordinances in place then contacting the police through their non emergency number can usually get the cops to show up and tell the neighbors to shut their dogs up or they will get a fine and/or have the dog or dogs taken away.
Many towns and cities have a noise ordinance that enforces the reasonable noise levels that a dog or other people can make and at certain times.
If the dog is barking constantly maybe try and speak with the neighbors and let them know nicely that the dogs barking constantly is bothering you.
If that doesn't work or you feel threatened by the neighbors then contact Animal Control or the Mayor of the town or city.
Police cannot do much if the dog is not actually causing any harm other than barking.
If you have a neighbors dog that won't shut up and quit barking and keeping you up at night or barking at you while you're in your yard then you will need to either call animal control if they have animal control in your area or call or contact the mayor.
If you don't have animal control then look up your mayors phone number and sometimes you'll be able to contact the mayor directly through their cell phone number and then you can make a complaint to the mayor about the issue.
Or you could show up at the next scheduled town or city meeting and voice your concerns at the meeting in front of the city council and mayor.
Sometimes the town may not yet have a noise ordinance in place and may need to put one in place and then the issue about the dogs barking can be enforced.
If the neighbors dog gets out of control and begins being aggressive and tries to attack you then contact 911 so that police can intervene.
But if it's just dogs barking then there's usually not much a police officer can do about the dog barking unless there's a noise ordinance that the dog is breaking.