My two brothers have worked at the local grocery store for years. It's unionized. Salaries are based on length of employment, with guaranteed raises each year. The position someone has doesn't affect their salary. However, the store is not going to let someone be a bagger for 10 years earning $15 / hour. They're either going to move him to another position or cut back his hours until he decides to quit. So in that sense, a bagger is the lowest paid employee.
Here, the position that pays the most is the night shift, as union rules demand time & a half pay. And to make more money, if a person is a very good employee, management will schedule him for every sunday, and any holiday he wants to work, as that again is time & a half pay per union rules.
So here, who gets paid more is not so much what position they hold, but when they are scheduled to work.