An Australian farmer is suing his neighbour after his farm was allegedly contaminated by genetically modified (GM) crops from the neighbour's farm.
Steve Marsh said he lost organic certification on 70% of his farm after GM canola seeds blew over from Michael Baxter's farm in 2010.
Mr Baxter's lawyers say the organic certifying body has unreasonable standards.
The trial has been described as a test case for farmers' rights.
The court case began in the Western Australian Supreme Court on Monday.
Mr Marsh's lawyer said it could be the "first court case of its type".
"It is important that farmers retain their rights to farm GM-free food as this in turn will protect consumers' ability to purchase GM-free food," lawyer Mark Walter said.
Mr Baxter's lawyers said that Australia's organic certifying body had excessive standards, and that Mr Marsh's farm was not contaminated since Mr Marsh grows oats and other crops, but not canola.
The case has divided the local community in Kojonup, Western Australia, where the two men were previously friends.
Various lobby groups have expressed support for the men.
The Safe Food Foundation is supporting Mr Marsh, arguing that the public have a right to eat GM-free food.
However, the Western Australian Pastoralists and Graziers Association said the case was "nothing more than anti-GM publicity" and that Mr Baxter did nothing other than growing a legal crop.
Both sides are reportedly raising funds to help support the men's legal fees.