Rivalry

The operative word in your question was NEW.

An established flock will almost always resist new members. Some more than others. Some flocks more than other flocks. Any time a bird is added, or removed, the pecking order is disrupted.

It is best to slowly introduce the new members rather than putting them together in daylight beak to beak.

Since you've already introduced the new birds to the flock, if the new birds are not being unduly hassled or being hazed to the point of bloodiness or to where they can't eat or drink, the pecking order is simply getting re-established and things will calm down soon.

If however life is miserable for your new members, I would recommend separating them out and using the fence divider and night addition method.

I've had good success by letting the new members run in my second pen (or subdivide your current one) with a divider of chicken wire. They can see each other but can't get to each other. After a few days or so, sometimes a week, once the existing flock generally ignores the new chickens, I then at night place the new chickens in the roost of the existing flock, close to calm birds. They generally wake up fairly integrated other than a few squabbles to remind everyone of their place. (It's as if they forgot who was who in the morning.)

You should also have little hiding places within your run and yard so that hens on the lower pecking order can get away from those who are higher and more aggressive.

If a bird is always over-pecked by the others, check its health as hens will generally attack those who are sick. If a bird is so aggressive as to be life threatening to others, I cull that bird. Pecking order is one thing; pecking to death is another.

My 2 cents from my experiences,
Lady of McCamley