This information can be obtained by an administrative subpoena (See an example of one at http://www.docstoc.com/docs/79005165/Administrative-Subpoena, notice they aren't required to list reasons such a subpoena would be invalid) or a police request, it's just that the hotel can choose to have a judge review the decision, and attempt to quash the subpoena.
What the supreme court said is that you can't arrest the hotel employee/owner for not handing over the information immediately, which was part of the LA law.
Good Coverage here: http://www.scotusblog.com/2015/06/opinion-analysis-an-opport...