A long-running dispute case between US-based biotech giant Monsanto and a Canadian canola grower is being heard in Canada’s Supreme Court.

The case centres on allegations by Monsanto that Saskatchewan farmer Percy Schmeiser grew Monsanto’s genetically engineered canola seeds without paying for them.

In 1997, Monsanto discovered that its biotech canola, engineered to withstand Monsanto’s weed killer, was growing on Schmeiser’s farm. Monsanto accused Schmeiser of obtaining the seeds without paying for them, but Schmeiser claims the canola took root on his farm accidentally. He claims the seed could have arrived on his farm by falling from a passing truck or blowing across from a neighbouring farm, reported The Associated Press.

The case has already been heard in two lower courts, which ruled in Monsanto’s favour and ordered Schmeiser to pay damages and legal costs.

The dispute has received attention from crop farmers around the world, who are afraid that if their conventional crops are accidentally contaminated with biotech crops, biotech firms will have the right to seize their crops.

Around half of Canada’s ten million acres of canola have been converted to Monsanto’s biotech variety since 1996, AP reported.