About 150 members and supporters of the Caroona Coal Action group are expected to march on Parliament in support of the Mining Amendment (Safeguarding Agricultural Land and Water) Bill which is due to be debated in NSW Parliament in the morning.

Under the Mining Amendment Bill, new mining developments and mining exploration on land defined as prime agricultural land will be prohibited.

The Bill will also protect land associated with rivers and aquifers that feed prime land.

"It is good to see the farm and environmental lobbies working together to protect prime agricultural land from mining," NSW Farmers' Association president Jock Laurie said.

"This has long been an issue for our Members, particularly those based on prime land such as the Liverpool Plains and the Gloucester Valley."

But NSW Farmers wants some changes to the terms of the Bill.

"While we certainly support the general framework of the Bill, it is important to note that we do not support the use of the existing NSW Department of Primary Industries (DPI) land classification system to define prime agricultural land, as this system is outdated and needs significant improvements," Mr Laurie said.

"We have asked for the Bill to be amended so that the definition of prime agricultural land and its water sources can be established by regulation at a future date.

"The regulation would use a new classification system developed in close consultation with the agricultural sector.

"This definitional issue should not delay passage of the Bill, however.

"The broad support for this Bill indicates that the time has come for Government to acknowledge the impacts of mining on agriculture and to provide legislation that ensures the sustainability of our most productive farming lands."

The rally will take place at the front gates of Parliament House at 10:30am on Thursday 4 June.