I suppose it depends on your language.

For example, if you're working in Java 8 where everything's just one big jumbled globally visible classpath, sure. If, on the other hand, you're working in Java 9 or later, you have the ability to control your public interface. People can get around that with reflection, so it's technically more permeable than a service boundary, but, if you're letting shenanigans like that sail past code review, you get what you deserve.