“In order to address a security-related issue related to encryption in one case, the authorities risk unlocking a Pandora’s Box that could have extremely damaging implications for the human rights of many millions of people, including their physical and financial security,” said Al Hussein.

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In what is widely seen as a test case for the future of digital encryption, Apple (AAPL) is resisting FBI pressure to unlock the iPhone of Syed Rizwan Farook, one of the shooters in December’s San Bernadino terrorist massacre. But Al Hussein urged the parties to consider the “potential wider impact” of such a move, saying that the case would determine “a key red line necessary to safeguard all of us from criminals and repression”.

Comment from a global human rights official is particularly relevant because of the increasing role of social media and smartphones in organizing political movements, from the Arab Spring to Black Lives Matter. In those contexts, Zeid said, strong encryption is foundational to “both freedom of expression and opinion,” and security weaknesses could lead to the persecution and even death of political activists.

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Zeid’s statement bolsters the position of the many U.S. tech companies who have sided with Apple. But polls show Americans split on the issue, with many supporting the government’s right to fight terrorism by any means. Even we here at Fortune have come to varying conclusions about who’s right and wrong, legally and ethically.

Al Hussein’s statement makes it clear how high the stakes are in the contentious debate, saying that “a successful case against Apple in the U.S. [would be] a gift to authoritarian regimes.”