Moscow has equipped more than 240 of its metro stations with a new system called Face Pay that uses facial recognition to charge passengers for their fare. It’s ostensibly more convenient than swiping a card or paying with a smartphone, but activists have reportedly expressed concern about the privacy implications of this widespread facial-scanning technology.

Moscow recently expanded its facial-recognition network with the addition of 175,000 surveillance cameras.

Face Pay further expands the reach of those facial-recognition systems. The system requires passengers to link their metro card, bank card, and a picture of their face using a mobile app. Moscow has reportedly said this data will be “securely encrypted” and that only interior ministry staff will have access to the servers on which it’s stored.

The introduction of Face Pay follows the European Parliament’s call to curb the use of biometric information, including facial recognition, in mass surveillance programs. The use of facial-recognition technology has also proven controversial in the US, where leading technology companies have called on lawmakers to better regulate the use of such tools.

Facial recognition has also become more common in consumer devices, however, most notably as an authentication method used by Apple in Face ID and Microsoft in Windows Hello. Face Pay sits at the intersection of government surveillance Moscow runs the metro service and the popularization of facial recognition software among ordinary people.

The city only expects 15% of metro passengers to start using the system over the next three years. As for the percentage whose faces will be scanned at each station, well, that number is probably much higher.