There is a difference, it's the threat that goes along with it, as in the Federation underlines that this is a blockade and that you'd better f-off outta here. The Empire is projecting its presence without outright barring access, like either a protector or a watcher.
Or a blockader. The fact that this is not communicated with the Empire gives it room for interpretation.
So basically, the Feds admit they are there for a blockade and the Empire tries to hide the fact that they are there for a blockade?
Well, if you're going to do something wrong at least be honest about it.