1. Yesterday the company fired a dozen people. They all got pink slips in their pay packets.
2. Gordon came home early from work looking worried. He had just gotten a pink slip, and now he would have to find another job.

The expression probably originates from the color of the form used to notify people that they had been fired. Such forms often came in multiple carbon copies. Each copy was a different color and was designated for a different recipient, e. g. , the pay office got one particular color, while the fired person always got the pink copy.