Just to clarify a point for discussion: this is already the law in the USA, and always has been [0]. European privacy law formerly prohibited private entities from reading personal communications, and handing them over warrantlessly to governments (as I understand it (?)); but this was never a thing in the US. [0] https://en.wikipedia.org/wiki/Third-party_doctrine
From that source: In 1986, the United States Congress updated the Omnibus Crime Control and Safe Streets Act of 1968 by enacting the Electronic Communications Privacy Act which included an updated "Wiretap Act" and also extended Fourth Amendment-like protections to electronic communications in Title II of the Electronic Communications Privacy Act, known as the Stored Communications Act . In Carpenter v. United States…
In 2010, the Sixth Circuit held ECPA to be unconstitutional as it relates to email and compelled disclosure without a warrant (at least for large volumes of private email) [0]. This hasn't been tested at the Supreme Court, although the Warshak opinion has been cited approvingly, mostly because providers don't disclose content without a warrant so nobody has had a case to take up.
Carpenter shows 4A can protect metadata under some circumstances too (for more than 7 days of CSLI), even if law enforcement obtain a court order, which requires less evidence than a search warrant.