Reservation is a postponement of conscription for military service during mobilization. Reserved employees of enterprises, institutions and organizations have the right to cross the border under martial law.
Reserved men can go abroad for a business trip, but return to Ukraine after the expiration of the term prescribed in the business trip order. A mandatory requirement is the availability of documents confirming the purpose of the trip, reservation documents and a military ticket.
That is, when crossing the border, a man must have with him a document confirming his legitimacy of staying abroad. And also a military registration document, which will state that the man has a reservation (or he is a student), that is, there is a reason for postponement of mobilization.