Unknown Republican Blocks Bill That Will Require Search Warrant Before Police Access Emails

An unknown Republican Senator is blocking a bill that will require police to obtain a search warrant before accessing emails and online messages.
The Hill reported:

An anonymous Republican senator has delayed a vote on legislation that would require police to obtain a warrant before accessing emails and other online messages.

Senate Judiciary Committee Chairman Patrick Leahy (D-Vt.) pushed for a vote on the bill before Congress left for its August recess. He secured unanimous support from Democrats, but at least one Republican objected to the bill, according to a Democratic Senate aide.

Leahy had hoped to fast-track the bill to passage with unanimous support, but the opposition means a vote will be delayed until at least September.

A Leahy aide said the senator will continue to work with Republicans to address their concerns. The Senate could pass the legislation without unanimous support, but it would take up valuable floor time to override a filibuster.

It is unclear which Republican or Republicans objected to the bill, S. 607.

Who would be against this? And, for what reason?