Their opponents include beverage and food giant, Coca-Cola Amatil, which wants to increase its extraction of spring water at Peats Ridge from 25 to 66 megalitres a year for a bottled water operation.

Coca-Cola has become a major supplier of spring water in recent years with its brands now including Peats Ridge, Neverfail, Mount Franklin, Taurina Spa and Deep Spring.

Gosford City Council, concerned about dwindling town water supplies, has rejected Coca-Cola's water application but the company has taken it to the Land and Environment Court.

A new sand mine proposed at Somersby by the Somersby Fields company is also causing friction, as are plans by existing sand mines to expand.

Land owners also fear further disruption from reported moves by Sydney Gas to explore in the area.

The unhappy landholders plan to voice their protests at a meeting at Mangrove Mountain on June 26.

Under Sydney Regional Environmental Plan number eight (SREP8), an area of about 90,000 hectares stretching from Calga to Peats Ridge, Mangrove Mountain and Somersby is dedicated to agriculture.

Properties cannot be sub-divided smaller than 20ha and no sub-division for residential development is allowed.

According to the NSW Department of Primary Industries, agricultural activities such as poultry, vegetable and fruit growing and nurseries in the area produce about $105 million worth of farm produce a year.

The plan was revised in 2001 to allow sand mining to feed SydneyÕs insatiable demand for building materials and there are now several mines on the plateau.