THE Greens have proposed an alliance with Tony Abbott's Coalition to support laws that would make it harder for coal-seam gas miners to intrude on farm land.

Seizing on comments Mr Abbott made defending the rights of farmers against miners, the Greens leader, Bob Brown, has promised introducing a private member's bill in the next fortnight that would restrict the access of miners to farmland.

Using corporations powers in the constitution, the bill would require a mining company to receive the written permission of the landholder before being able to explore for, or extract, coal-seam gas.

The issue has become politically explosive in NSW and Queensland where a proliferation of coal-seam gas wells has resulted in miners being accused of riding roughshod over farmers under state law.

Under the law, the farmer owns only the top layer of soil, while that underneath belongs to the Crown and a farmer is powerless to impede access to the property.