Eastern Orthodoxy teaches the essence–energies distinction of God. Wikipedia quotes catholic-church.org's explanation:
The Ultimate Reality and Meaning of the Palamite theology consists of the distinction between God’s Essence and Energy. This is a way of expressing the idea that the transcendent God remains eternally hidden in His Essence, but at the same time that God also seeks to communicate and The Distinction between God’s Essence and Energy unite Himself with us personally through His Energy.
This sounds very similar to how theologians since Athanasius have spoken of the difference between the ontological (or immanent) and the economic views of the Trinity. R. C. Sproul explains:
Ontology is the study of being. When we talk about the ontological Trinity, or as some theologians term it, the “immanent Trinity,” we are referring to the Trinity in itself, without regard to God’s works of creation and redemption. In the Trinity, there are three persons —the Father, the Son, and the Holy Spirit—who together are one being. The ontological structure of the Trinity is a unity (Deut. 6:4). When we speak of the economic Trinity, on the other hand, we are dealing with the activity of God and the roles of the three persons with regard to creation and redemption.
But while Catholics and Protestants generally accept the ontological/economic views of God, they regard the essence–energies distinction as problematic or even heretical.
So what is the difference between these views, and why would many Western theologians consider the essence–energies distinction to be heresy?