Chris Soghoian points us all to an invited brief on the issue, submitted by the ACLU/NYCLU. Here’s a snippet from it:
Even if this Court does not read the SCA or the Fourth Amendment to prohibit the government from seeking tower dump authorizations in all circumstances, it should conclude that tower dumps require the judicial oversight provided by a probable cause warrant. The SCA provides magistrate judges with the discretion to require the government to apply for a warrant pursuant to 18 U.S.C. § 2703(c)(1)(A) instead of an order pursuant to § 2703(c)(1)(B) and § 2703(d). To avoid running afoul of the Supreme Court’s skepticism about the constitutionality of “dragnet type” location tracking of large numbers of people, this Court should require the government to proceed via the SCA’s warrant mechanism. Recourse to a warrant is also required because the government cannot meet the SCA’s reasonable suspicion and relevance standards when it seeks records relating primarily to a group of non-suspects.
Thus, at a minimum, the government must demonstrate probable cause that the tower dump will turn up evidence of a crime, and any warrant issued pursuant to the SCA and Rule 41 must enforce the Fourth Amendment’s particularity requirement by minimizing the number of innocent people whose records are sought and by restricting the government’s retention and use of any third party records included in the tower dump. A warrant must also require notice to all persons whose location information and other records the government obtains.
Read more here.