Wool is harvested through a process called shearing. (It's like getting a 'number 4' haircut.)
Shearers are highly skilled people and pride themselves on careful handling of the sheep. They leave a good covering of wool on the sheep, to keep them warm. Machine shears are the most popular tool for shearing, as they are fast and efficient, for minimal stress on the animal.
Sheep have been bred for thousands of years to grow wool, therefore shearing is not just about harvesting wool — it's also about keeping the animals comfortable, relieving them from having to endure the hot summer months with a heavy fleece.
As part of being certified, the farms are third party audited including random audits conducted during the shearing season.