You're more likely thinking of Quakers. At least those still a part of the mid-Atlantic tradition historically use "thou" to avoid power distinctions. Not many

You're more likely thinking of Quakers. At least those still a part of the mid-Atlantic tradition historically use "thou" to avoid power distinctions. Not many still do this in daily speech, but it's not absolutely lost, and is sometimes used for emphasis in a conversation in which matters of power and equality are lurking.