They are fighting plans by Worthing council to sell off land next to Iron Age hill fort Cissbury Ring.
The campaign's efforts have forced the authority to announce it is rethinking its plans, but protesters are warning this is just a ruse.
At a meeting on Thursday December 3, the council cabinet will be meeting to discuss disposing of the land on a 99-year lease, rather than actually selling it.
Stop the Cissbury Sell-Off is calling for a protest outside the Town Hall in Chapel Road, Worthing, at 6.30pm and for people to attend the meeting at 7pm as well.
Said a SCSO spokesman: "Despite what you may have heard, Worthing Borough Council have NOT abandoned their plans to sell off land close to Cissbury Ring.
"Indeed, they have said that they will now sell 'long term leases instead of selling the freehold of our buildings and land'.
"That will mean any buyer will consider themselves the new owner - just the same as you would if you bought a leasehold flat with a 99 year lease.
"That means that full public access and enhanced conservation management of our public downland will be ‘out the window’ unless we act now to make council leaders change direction."
Hundreds of residents protested against the controversial council plans on November 14.
They then filed up on to the land itself, waving banners and placards, and let off distress flares to draw attention to the threat.
Further information on the campaign, including maps of the land in question, can be found on the
SCSO website at www.scso.co.uk. To contact the group email  info@scso.co.uk