If you are collecting unemployment and you worked one day out of your two weeks period do you need to report it and if you have not yet what will happen when you do?

Emphatically, YES. Any income you receive, no matter how small needs to be reported. What happens if you don't? Pay back your benefits + penalties + interest and loss of future earnings credit and possible denial of future benefits. Besides all that you are subject to criminal prosecution for unemployment fraud. See the Related Link below for more information.