On Wednesday, the supreme court will consider whether the government must obtain a warrant before accessing the rich trove of data that cellphone providers collect about cellphone users’ movements. Among scholars and campaigners, there is broad agreement that the case could yield the most consequential privacy ruling in a generation.

Less appreciated is the significance of the case for rights protected by the first amendment. The parties’ briefs make little mention of the first amendment, instead framing the dispute – for understandable reasons – as one about the right to privacy. Yet the court’s resolution of the case is likely to have far-reaching implications for the freedoms of speech, press and association.

The case, Carpenter v United States, arises out of the government’s prosecution of Timothy Carpenter for a series of armed robberies carried out in south-eastern Michigan and north-western Ohio several years ago. In the course of its investigation of the crimes, the government ordered Carpenter’s cellphone provider to turn over data it had collected relating to Carpenter’s movements. In response, the provider produced 186 pages listing every call that Carpenter had made over a 127-day period, as well as coordinates indicating where Carpenter had been at the beginning and end of each of those calls.

Importantly, it turned over these records even though the government had not obtained a warrant based on probable cause. Carpenter asked the court to suppress the government’s evidence under the fourth amendment, which protects the right to privacy.

Many cellphone users have only a vague understanding of the extent to which providers monitor their movements, but these companies now track us much more closely than even the most committed human spies ever could. Cellphones function by connecting to antennas – “cell sites” or “cell towers” – that provide cellular service. Those cell sites, which are owned and operated by the cellular companies, are programmed to record which phones connect to them, and when. They also record the direction from which the connecting phone’s signal is received and, often, the distance of the phone from the cell site.

So-called “cell site location information” is becoming ever more precise, because the cellular network is becoming ever more dense. The analytical tools that can be brought to bear on this information are also becoming more sophisticated, meaning that investigators can draw reliable conclusions from smaller and smaller amounts of data. It’s precisely because the information is so rich, of course, that the government is interested in accessing it.

Privacy scholars are watching Carpenter’s case closely because it may require the supreme court to address the scope and continuing relevance of the “third-party-records doctrine”, a judicially developed rule that has sometimes been understood to mean that a person surrenders her constitutional privacy interest in information that she turns over to a third party. The government contends that Carpenter lacks a constitutionally protected privacy interest in his location data because his cellphone was continually sharing that data with his cellphone provider.

Privacy advocates are rightly alarmed by this argument. Much of the digital technology all of us rely on today requires us to share information passively with third parties. Visiting a website, sending an email, buying a book online – all of these things require sharing sensitive data with internet service providers, merchants, banks and others. If this kind of commonplace and unavoidable information-sharing is sufficient to extinguish constitutional privacy rights, the digital-age fourth amendment will soon be a dead letter.

To understand the Carpenter case’s full significance, though, it’s necessary to consider the implications the government’s arguments have for first amendment rights. In a brief filed in support of Carpenter, 19 leading technologists explain how easy it is to use a person’s location data to learn about her beliefs and associations. (We represent the technologists.) With very few data points, the technologists observe, an analyst can learn whether a given person attended a public demonstration, attended a political meeting, or met with a particular activist or lawyer. With more data, an analyst can identify social networks and learn not only whether a given person was at a public demonstration but who else attended the demonstration with her.

Journalists and their sources might be at particular risk. Imagine parallel demands for the cell site location information of a journalist who exposed government misconduct and of all the government employees who had access to the information the journalist exposed. As the Reporters Committee for Freedom of the Press observes in its own brief filed in the Carpenter case, cell site location information “can reveal the stories a journalist is working on before they are published, where a journalist went to gather information for those stories, and the identity of a journalist’s sources”.

This is why it is a mistake to think about the Carpenter case solely through the lens of individual privacy. A defeat for Carpenter would be a defeat for privacy rights, but it would also mean a dramatic curtailment of first amendment freedoms.

The Carpenter case is the latest in a series of cases that have required the supreme court to consider the relevance of analog-era precedents to digital-age technologies. Although these cases were presented to the court as fourth amendment cases, the court was attentive to the implications of government surveillance for first amendment freedoms. When the court held that the fourth amendment precluded the government from installing a GPS device on a criminal suspect’s car without first obtaining a warrant, five justices cited some of the same concerns raised by the technologists we represent in Carpenter.

Do “people reasonably expect that their movements will be recorded and aggregated in a manner that enables the government to ascertain, more or less at will, their political and religious beliefs [and] sexual habits?” Justice Sonia Sotomayor asked in her powerful concurrence.

Two years later, when the court ruled that the government could not search a criminal suspect’s cellphone without first obtaining a warrant, the court cited similar concerns.

“Awareness that the government may be watching chills associational and expressive freedoms,” Chief Justice John Roberts wrote. Left unchecked, he warned, new forms of surveillance could “alter the relationship between citizen and government in a way that is inimical to democratic society”.

The court was right in these cases to take account of the implications of surveillance technology for rights protected by the first amendment. It should be similarly attentive to these implications in Carpenter. Without strong protections for individual privacy, the freedoms of speech, association and the press will wither.

In assessing whether Carpenter had a right to privacy in his location information, the court should consider what will remain of these indispensable democratic freedoms if the government is afforded access, without close judicial supervision, to the information that cellphone providers are continuously collecting about all of us, and to the other sensitive and even intimate records that all of us passively and routinely share with third parties.