Korean company Cockatoo Coal wants to drill 120 holes as part of a bore testing scheme in the area of Sutton Forest, where the Hollywood actress and her country singer husband own an expansive estate.

Many residents are furious about the plans, and now the celebrity couple has added its weight to the campaign.

Kidman and Urban recently bought a sign from a local market, and have pinned the placard on the gates of their property, reports The Sunday Telegraph.

Peter Martin, the Southern Highlands Coal Action Group convener, says, ""We sold them the sign for $20 when they visited the Moss Vale Farmers Market one Saturday morning on their last visit here.""