A two-day pre-trial hearing starts today in Whakatāne District Court for Worksafe's Whakaari/White Island prosecution.
The volcano eruption killed 22 people and left 25 others seriously injured in December 2019.
Thirteen parties are facing charges over allegedly failing to meet their health and safety obligations to workers and visitors.
Those parties include 10 organisations and three individuals in the Buttle family, which owns the island.
Among the organisations are White Island Tours, GNS Science and several helicopter agencies whose pilots went onto the island to save injured and dying people.
However, a petition to drop charges against the pilots, dubbed "heroes", has received more than 138,000 signatures.
Today's proceedings will be live streamed to families and victims around the world, with many of those caught up in the disaster being overseas tourists.
The defendants are not required in court today, but it is possible they will enter pleas.