1. Steve is going to run into trouble if he continues to arrive late at work. He’s on thin ice with the boss already because he spends more time talking on the phone than working.
2. Anita is in serious trouble at the university. Her grades are poor and unless she does well on her final exams, she may be skating on thin ice.

The expression suggests how dangerous it is to tread (walk) or skate on ice that, although frozen, is not thick enough to support one’s weight.