Been there, got the T-shirt, been escorted off the premises (for sending personal emails on work time), whilst working for large US corp. This was over 15 years ago when I was starting out and I learned a very valuable lesson.
If you are a 'trouble maker' i.e. someone who asks too many undesirable questions or rocks the boat, then HR will find a way to fire you. Your work contract protects them and not you.