The New Zealand Drug Detection Agency (TDDA) says employees are trying to trick substance tests at work "almost daily".
Employers can require workers to take drug tests if they work in safety-sensitive jobs but there are products available - such as fake urine - to trick those tests.
"There is a significant amount of people who try and cheat the test, almost on a daily basis," TDDA group technical manager Rod Dale told The Project on Wednesday.
Employers say drug testing at work is to keep people safe and prevent accidents or deaths, and don't want kits that trick the tests to be accessible. They are readily available from retailers such as Cosmic.
"My experience with these kits is very limited," employer Matt Punter said. "I didn't know they existed until very recently.
"Why should I have to be personally liable for accidents that happen, when this product is out there making it harder for me to prevent it from happening?"
The Project asked Cosmic to appear on Wednesday night's show to discuss the products but declined.
New Zealand Drug Foundation executive director Ross Bell said people are trying to get around the system because of trust issues in the workplace.
"It's [drug tests] not the making of a good employment relationship," he said.
"Again, this is where workplaces shouldn't be relying on these invasive tests to build a good health and safety culture in the workplace.
"I think when you're asking your staff to wee into a cup, you've got bigger issues around the health and safety culture in your workplace."