What is the correct word or words that matches the given info?

Question

Good day! What is the word that describes a person who operates within a specific land or area without the permission of the owner of that area/ land?

In case it might help, here's the background of my question: In our province, we own a land that is mainly used for agricultural purposes, but there is also a group of people who tends to invade it and harvest it for themselves, and planting their own crops there. We legally own the place. Now we want to right a formal letter directly to our central government to request aid for this issue, but we are having a hard time coming up with a word that best describes the situation.

Answer 1

I think Squatter fits this bill nicely!

From dictionary.com:

a person who settles on land or occupies property without title, right, or payment of rent.

Answer 2

I think the proper term is OCCUPIER.

According to Collin's Dictionary (https://www.collinsdictionary.com/dictionary/english/occupier):

"The occupier of a house, flat, or piece of land is the person who lives or works there.

[formal]"

According to Oxford English Dictionary (https://en.oxforddictionaries.com/definition/occupier):

occupier

// A person or company residing in or using a property as its owner or tenant, or (illegally) as a squatter.

There's another word with the exact sense of this action illegality -

trespasser

A person entering someone's land or property without permission.

‘a trespasser on his land’

(https://en.oxforddictionaries.com/definition/trespasser)

Here's an example from Reverso.context.net:

'You are a trespasser in my poppy fields.'