The phrase "duty work" typically refers to one's responsibilities or tasks that they are obligated to complete. It implies work that one must do as part of their job or role. Full definition
This is the epitome of a heavy duty work truck. (cars.oodle.com)
The employer may even look for a reason to terminate you so if you are back to work on light duty work restrictions, so you need to be on your best behavior! (injuredworkerslawfirm.com)
The cons of this vehicle have been few and far between in my eyes when looking at a heavy - duty work truck. (autolist.com)