It looks like Shamblesmaybe made an attempt to answer this question in another thread:
Really? I’ve asked twice in that other thread for the law being broken, and you have yet to respond.
How’s this for a quick start?
The Occupying Power shall not deport or transfer parts of its own civilian population into the territory it occupies.
From
http://www.btselem.org/english/settlements/international_law.asp
But, as has also been pointed out in that thread, that particular ruling forbids the government from establishing settlements, not private citizens.