Operations have started at an opencast mine site in Shropshire where eco-protesters have assembled.
UK Coal has been setting up a secure area at New Works, near Lawley in Telford, with the help of police.
UK Coal said it had spoken to activists to explain they were not being moved on as an eviction order had not yet been obtained. Demonstrators moved on to the site in January.
West Mercia Police said officers were there as a precaution.
UK Coal said it was working on a part of the site where eco-protesters are not camped.
Asked about the mood, one activist, Ben, said: "Determined, I'd say. If you don't try and fight, then you can't win."
Asked about what would happen next, he said: "We're going to build defences and obviously people will be coming along to help out and wait and see if they serve papers."
The protestors said they had already built tunnels 2ft wide (60cms) which expanded into larger underground living chambers, fitted with steel doors, from which to continue their protest.
Diggers have been brought in to prepare the ground for mining work to start.
Dave Bolton, from UK Coal said: "I am not concerned about where they [the protesters] are, they won't get in my way for quite a while, it's not a short-term issue for me."
Campaigners are being warned not to trespass on the secured area of the site.
UK Coal was granted permission last year to extract 900,000 tonnes of coal from the site, near The Wrekin, over 32 months.
Residents opposed the original application by UK Coal and the project was referred to a planning inspector in 2008.
Plans were approved in October 2009 after a public inquiry in April last year.
The Wrekin is a tree-covered hill that stands about 400m (1,330ft) above sea level.
UK Coal has pledged to return the site to green fields within four years of starting mining operations.
The mine will provide 90 new jobs, the firm has said.