The Ministry of Business, Innovation and Employment says more than half of all the dairy farms it has investigated are in breach of employment laws.
Ministry officials visited 44 farms and found 31 did not measure up.
The ministry says most of the breaches relate to insufficient record keeping.
It says farmers need to keep accurate time and wage records to ensure they meet their obligations for minimum wage and holiday payments.
The ministry has ordered 23 farms to improve their work.
Several cases are still open and could face more serious consequences.
The offending farmers have been given 28 days to comply and the ministry plans to check on them again.