Greens minister Shane Rattenbury has broken ranks with his cabinet colleagues and called on the ACT government to divest its shares in the company behind the Maules Creek open-cut coalmine.

Mr Rattenbury last week visited the Leard State Forest in north-west New South Wales, where Whitehaven Coal is planning the $767 million mine.

A protest at Maules Creek coalmine earlier this month.

Land clearing is under way at the site and the first coal moving is expected to come as soon as January 2015.

The project has been a flashpoint for local campaigners and anti-coal protesters, including at Whitehaven's annual general meeting in Sydney last month.