A ruling found that coercing suspects to open their phones using biometrics violates the fourth and fifth amendments. The ruling comes from a Jan. 10 filing, for which police were seeking a search warrant as part of a cyber-extortion case. Law enforcement wanted to use the warrant to search through suspects belongings including unlocking any devices on the premises via fingerprinting or facial recognition. That would mean compelling the suspects to use their fingers or other biometric features to unlock their personal devices.
Source: https://threatpost.com/judge-law-iphone-unlock-faceid/140856/