"Joining the ALP will help us follow best practice in an area that is full of conflicting advice and regulations," said Andy Ferguson, HR and health and safety manager.
"The amount of temporary labour we use, when averaged out, is equivalent to approximately 100 additional employees."
ALP, for groups using temporary, contract and seasonal workers, recently launched a Gangmaster Audit Tool software program to check firms providing labour.
Gangmasters and temporary labour were "highly sensitive areas" for Greenvale's larger customers, said Ferguson.
"The Gangmaster Audit Tool allows us to accurately audit the supplier and show our customers that our worker policies follow best practice.
"Greenvale needs to ensure that, despite GLA certification, our labour providers are complying with the standard.
"We wanted to find a cost-effective and transparent system that would give labour users, labour providers and workers the protection they need."