From Ann Groninger's "Ride Guide" book on NC cycling laws and cycling safety (https://www.bikewalknc.org/wp-content/uploads/2020/01/BIKELAW_RG_NC_2019_WEB.pdf)...
"GROUP RIDING
Benefits of group riding: Many bicyclists who ride recreationally enjoy riding in groups. Group rides are a great way to interact with friends and enjoy the outdoors at the same time. They also help with training, as riders push each other and work to get stronger.
Riding next to another bicyclist or group of bicyclists does take up more space and therefore makes you more visible, which is safer. Also, a group of bicyclists will usually occupy the lane, requiring motorists to wait until they can safely pass in the next lane.
The downside: Bicycle group riding is a popular activity around the state and is growing. Yet when you hear motorists complain about bicyclists, the complaint you hear most often is about the “group of 50 cyclists blocking rush hour traffic” or a similar complaint about a large group. You get the idea. So what is the law on group riding, and how do you square group riding with the concepts of safety and courtesy we have discussed already?
Group rides and riding two abreast is legal: First, there is no state law addressing group riding. Anyone who tells you the law requires you to ride single file is incorrect except in very limited places, typically designated by county or municipality. On almost all
roads, riding two abreast is perfectly legal. Some municipalities have “no more than two abreast” ordinances that are often mistaken for requiring single file riding. Check out your municipal code at www. municode.com to see if there are any areas that apply to your ride.
You may sometimes hear motorists say that bicyclists should ride single file, as a courtesy to motorists. By doing so, the bicyclists sacrifice some of their safety advantage by allowing motorists to pass in the same lane. Also, it is not necessarily true that it is easier for motorists to pass bicyclists riding single file. Six bicyclists riding two abreast are (very roughly) about the length of two and one-half cars; at single file, they are twice that length and require more time to drive around. Riding two abreast also increases the group’s efficiency at intersections.
There is no law obligating bicyclists to make passing easy for motor vehicle drivers. A smart and courteous bicyclist, however, chooses his or her route and bicycling time wisely. If riding recreationally, it is preferable to choose as many lesser traveled routes as possible or routes where it is easier for motorists to pass, if possible, and
not ride lengthy stretches of congested arterials during rush hour traffic. Since our roads and neighborhoods are not typically built with bicycle connectivity in mind, it is not always possible to avoid busier roads. As a bicyclist you have the absolute legal right to use the road as you wish, within the rules of the road. You have an obligation to others – including other bicyclists who will share your reputation – to use your rights wisely."
BRBC Ride Leaders rarely have their groups ride two abreast (even though it would be safer for all the riders) and attempt (but not always successfully) to break larger groups into smaller groups to minimize impeding traffic and not add to motorists ire with cyclists.