Can Verizon wireless sim lock the iPhone 5 if bill is unpaid?

So the iPhone 5 will be sim unlocked. What if I cannot pay the bill when it is due or it is passed due date? Will they be able to all of a sudden lock the sim slot to their carrier?

Added (1). First answerer did not answer my question: if I pay late, will they relock the sim card? Obviously they will disconnect my service.

If you don't pay your bill, they cut off your service. Simple.