The Department of Labour says almost a third of farms it has visited over the past two months have not been following quad bike safety rules.
Health and Safety inspectors have visited more than 370 farms as part of the department's quad bike safety campaign launched last year.
It has given 117 farmers either written warnings or issued them with improvement notices.
The Department's Chief Adviser of Health and Safety, Dr Geraint Emrys, says helmet use was one of the biggest areas of non-compliance.
Each year about 850 people are injured while riding quad bikes on farms.