You can't stop the Imperial Stormtroopers. George Lucas sued the original designer of the stormtrooper costumes in Star Wars, seeking to stop him selling replicas. But even though Lucas prevailed in a U.S. court, he lost in the U.K.
Andrew Ainsworth built the original costumes in the first movie, and he argued in court that they were mass-produced and utilitarian. And this paid off. As attorney Simon Bennett explained to the Guardian:
The judges concluded that the helmet could not be regarded as an artistic work because it was a mass produced item - remember how many stormtroopers there were? - and has an utilitarian role.
However, the fact that Ainsworth lost his case in the U.S. means that Lucas could sue him in the U.K. for "infringement of foreign copyright," said Bennett. [Guardian]