Do you know where the power line easement boundary is? If not, ask them to provide a plan showing the easement.
They have no right to require you to remove the whole tree, but only the portion that is trespassing. Nevertheless, pines grow fast and you may end up removing the tree if too much of it encroaches. if you can still transplant them, you may want to move them far enough away that you can keep them out of the right of way by pruning.
The foregoing answer does not constitute legal advice and does not create a lawyer-client relationship. Answers are based upon the facts stated and may change if there are additional facts not contained in the question.