It is an emotive subject with fishermen.
Many nets are legal. Whilst anglers might not agree with them, if they are entitled to fish that way, they are entitled to fish that way. We have to respect that.
However, if you think a net is illegal e.g. in a place it should not be or not correctly labelled, my understanding is the action is to report it to the EA (0800 807060 anonymous).
Do not confront a netter or take direct action, leave it to the experts.