It doesn’t matter which heading. It could even be under legal.
I would probably classify it as economic.
The importance of PESTEL is to get you to go through a checklist that will help you to identify potentially relevant environmental factors. Once you have identified minimum wages you can then look at the potential effects on the company such as:
1 Increased costs in the country 2 Stronger competition from firms in countries without minimum wage laws 3 Fines and penalties if the minimum rate had not been paid.