INAL, but if the authorities had captured your device with touchID enabled and legally ask you to use it to login and you do an action that would disable touchID, then that would be "obstruction".
You're thinking more along the lines that they ask you to touch the sensor and you use your fingernail razor blades to damage the sensor or something like that.
Others had floated the idea of locking by using an alternate finger with touchID, after the fact.