The Fourth and Sixth Amendments prohibit government officials from in any way intruding on the privacy of lawyer/client confidential rights of citizens.
The very fact that this material is seen or read by a government official constitutes a core violation. It would be the same if the government surreptitiously recorded a confession of a penitent to a priest, or a description of symptoms by a patient to a doctor, or a discussion of their sex life between a husband and wife.
The recourses for intrusions on the Fourth and Sixth Amendments are multifold: the victim of the intrusion can sue for damages; he or she can exclude it from use by the government in criminal or civil cases; or the victim can demand the material back. But none of these remedies undo the harm to privacy and confidentiality done to the citizen by the government’s intrusion into his private and confidential affairs.