While warehouse workers could file suit under the National Labor Relations Act if fired for speaking publicly of their own working conditions, I'm not sure that Amazon's UX team would qualify (but again, IANAL).
To draw an analogy: Would a DoorDash engineer be safe speaking out against the working conditions of DoorDash drivers?
They should be, but you might be right that the National Labor Relations Act (or other applicable law) isn't doing its job.