A group called Brighton Climate Action is squatting in a disused school in Lewes.
The group is threatening to take direct action against businesses that it says are damaging the environment, including the Newhaven incinerator and Gatwick airport.
It also said that it would target high street shops accused of tax avoidance.
The group plans a May Day protest and day of action in Brighton next Sunday (1 May).
It intends to spend much of this week exchanging ideas about how to carry out effective direct action.
Some 40 people are believed to be taking part in the squat at the old St Anne’s School site in Rotten Row, Lewes.
The disused school is in the shadow of East Sussex County Council’s County Hall headquarters.
The council said that it was monitoring the situation and liaising with Sussex Police.
The squatters said that they intend to stay until Sunday.
They are aware that, with the Easter bank holiday today and the Royal Wedding public holiday on Friday, it would be difficult for a court-enforced eviction before then.
The group’s website says: “The South Coast Climate Camp is popping up in Sussex to highlight the climate criminals along our coastline.
“We have drilling for oil in the South Downs National Park, an agrofuels plant proposed for Shoreham Harbour, proposed airport expansion and of course the incinerator in Newhaven.
“All this climate criminality not only adds to the outrageous levels of greenhouse gases spewing into the atmosphere, it also despoils our national parks and generally charming countryside.
“It ain’t right. Something needs to be done.
“The South Coast Camp for Climate Action will take place from the Easter weekend through to the May Day celebrations.
“Through living, eating and working together, we hope the camp will act as a positive catalyst for change, transforming both the camp community and the communities around it.”
Catering at the squat is being organised by the new Brighton front-line catering group called Revolting Vegetables
