In other words, don't enable touch id or face unlock.
Here: https://blogs.wsj.com/digits/2014/10/31/judge-rules-suspect-...
Unsure about federal application, actually. We as country need to get our shit together regarding device privacy. You should need a warrant to look at a phone, laptop, whatever, with or without a password. The security of the device should be meaningless.
As for me, I'm grateful that I have the resources to push back should this ever happen to me, jailtime or included. That's a luxury probably very few Americans can realistically afford (seeing as they can just throw you in jail for 48 hours).
I believe the rationale was that they can't ask you to incriminate yourself (give up your passcode), but you don't have to say anything for them to force you to give your fingerprint.
That said, you shouldn't ever rely solely on biometrics. In addition to the legal reason, an adversary could also unlock your phone if you were unconscious / etc using your thumb.