A petrochemical company is threatening legal action over the National Trust's refusal to allow testing for shale gas on its land.
Ineos wants to conduct seismic surveys at Clumber Park in Nottinghamshire to see if there is potential for fracking.
The firm said the charity had blocked any contact for almost a year and it was considering seeking a court order.
The National Trust said it opposed any activities leading to the extraction of fossil fuels, so rejected requests.
Moves to look for shale gas in the Sherwood Forest area have proved controversial due to environmental concerns over extraction - known as fracking - and expansion of fossil fuel use.
Ineos said it already had permission from nearby landowners for the the non-invasive survey and its ability to extract gas would be "significantly limited" if it could not get on to Clumber Park.
"If the National Trust refuses to change its position, Ineos will have no choice but to write to the Oil and Gas Authority, asking for permission to seek a court order enforcing its rights to carry out these surveys on National Trust land," it said in a statement.
The company said government licences gave it a legal obligation to investigate shale gas deposits around the country and criticised the charity's position as "overtly political" as shale gas had lower carbon emissions than either oil and gas.
A National Trust spokesman said: "The National Trust is opposed to fracking on its land and will reject any fracking requests or inquiries.
"Consistent with this, we say no to surveying on our land for fracking purposes."