Protesters hacked the website of mining company Solid Energy on Friday.
The website was altered to redirect visitors to a video opposing lignite mining.
The video showed 100% Pure New Zealand advertisements contrasted with images of coal mining and contained a link to the Aotearoa Coal Action Network.
The network says it does not know who hacked the website but it supports any form of non-violent protest against lignite mining.
Solid Energy says the hackers broke the law and the company will refer the matter to police.