The Defence Force says 94 staff across the whole military are on leave without pay, and it does not know many may be in Ukraine.
It said it has begun contacting all soldiers on leave without pay to remind them they cannot go to Ukraine.
It comes after NZ Army soldier Dominic Abelen was killed fighting Russian forces while on leave from the army.
Defence Force (NZDF) rules prevented the 28-year-old corporal from going to Ukraine, and he had not told them about his plans.
NZDF said it has begun contacting all soldiers on leave without pay to remind them they cannot go to the country.