See Zurcher v. Stanford Daily, 436 U.S. 547 (1978) in which the United States Supreme Court held that (in summary):
A State is not prevented by the Fourth and Fourteenth Amendments from issuing a warrant to search for evidence simply because the owner or possessor of the place to be searched is not reasonably suspected of criminal involvement. The critical element in a reasonable search is not that the property owner is suspected of crime, but that there is reasonable cause to believe that the "things" to be searched for and seized are located on the property to which entry is sought.
That established the constitutional floor. However, Congress responded by providing additional protections to journalists via the Privacy Protection Act of 1980 (see generally [ref]). It requires government officials to rely on subpoena rather than a warrant and search and seizure when seeking information from reporters (when those reporters themselves are not suspects of the crime):
[n]otwithstanding any other law,representatives of the government may not search a newsroom for the purpose of obtaining work product or documentary materials relating to a criminal investigation or criminal offense, if there is reason to believe that the work product belongs to someone who will publish it in a "public communication, in or affecting interstate or foreign commerce
All of that has to be read in the context of what a Fourth Amendment search is. A search here is when there is a violation of one's reasonable expectation of privacy (or, post-Jones, also would include a trespassory search). If the person in control of the newsroom and its contents consents to the "search" it's not even a Fourth Amendment search (although somewhat confusingly, it's also referred to as a "consent search").