They were accused of 'spying' for a foreign government.
a 'spy' camera/plane [=a camera/plane used for spying]
a 'spy' novel/thriller [=a novel/thriller about spies]
(..) My company are those loyal to Rohan. And for that, we are banished. The White Wizard is cunning. He walks here and there, they say... ...as an old man hooded and cloaked. And everywhere, his spies slip past our nets. We are no spies. We track a party of Uruk-hai westward across the plain. (..)2002 The Lord of the Rings: The Two Towers