Is it permissible to deal with companies that were nationalized and confiscated unjustly 50 years ago, and are they considered usurped property?

Usurpation (Ghasb) is the act of taking something by force and injustice. Ibn Juzayy defined it as taking possession of an owner's property or its benefit without the owner's permission, by way of dominance. The Shafi'is defined it as seizing another's right aggressively, and this includes what kings and bandits take unjustly.

Nationalization in socialist systems is considered usurpation. The usurper must return the usurped item itself, based on the Prophet's (peace be upon him) saying: "The hand is responsible for what it takes until it returns it." He must return it along with any increases, whether attached or separate. It is forbidden for anyone who knows that an item is usurped to deal in it through purchase or lease, because that is aiding the usurper, and the prolonged duration of usurpation does not nullify the right of the original owner.