Original trope here; a comment left on the original posting of it was: “What’s happened to people who try to claim that those microbes are weapons?”
I reply thus:
“A weaponized microbe in an appropriate warhead or containment packaging is freight.”
“A weaponized microbe in your gut/skin/breath/etc., on the other hand, is an act of biological or ecological warfare, and therefore an act of war or terrorism. Your confession is appreciated.”
Boom.
Decontamination Chamber: Fortunately, these days, it just involves a light mist of nanites checking you out (while clothed, so no fanservice, alas), but it’s routine protocol for (physically) entering a new habitat or, indeed, planet, given the risks of disease and, worse, ecological contamination.
It probably tells you everything you need to know about the Empire that you can bring all the weapons you like along on interstellar trips, but gods help you should you smuggle a single unauthorized microbe…