Shape up or ship out
Definition 1 of 1
Pro Tip 1/3Workplace Warning
Used by management as a strong warning to improve or face consequences. 
The boss said I need to shape up or ship out, so I'm really focusing on my punctuality now.
Pro Tip 2/3Not Literal
Usually not meant literally; more about improvement rather than actual leaving. 
My trainer told me to shape up or ship out, but she just wants me to work harder at the gym.
Pro Tip 3/3Ultimatum Context
Indicates a last chance; there may not be further warnings given. 
This is your last chance. You better shape up or ship out!