In central region, about 7 per cent of 10,216 tests were positive.
There, similar ratios of drugs were found: 73 per cent for cannabis, 11 per cent for opiates, 15 per cent for amphetamine-based drugs and 1 per cent for benzodiazepine.
Central region general manager Jason Trembath estimated up to 400 tests were done in Masterton workplaces every year, with most clients in the forestry industry, and some growth in civil engineering.
Mr Trembath said the figures indicated both more drug use, and more people getting caught.
"As we pick up more clients naturally you assume we're going to find more people. But there's no doubt about it, it's a continuing scourge on society," he said.
Some employees tried to cheat the tests using synthetic urine, which could be bought for about $60.
Forest Owners Association (FOA) board member Sheldon Drummond said drug screening has made a big impact on work culture in forests.
"Our non-negative rates have gone from about 20 per cent when we started testing to about 12 per cent," he said.
Mr Drummond, who is also chairman of the FOA's health, safety and training committee, said New Zealand had an issue with drugs and alcohol, and the forestry sector was not immune to it.
"But we're in safety-sensitive positions out there, and we can't afford not to be taking all practical steps."
FOA chief executive David Rhodes said many workers wanted to be part of those forestry gangs with a culture of being drug-free. "They have greater productivity, they're more efficient and it's just about safety really."
NZDDA chief executive Kirk Hardy said the company was careful to make sure employees gave informed consent and the tests were accurate. "You're talking about people's livelihoods, we can't afford to get a test wrong, people's reputations are at stake."
Department of Labour does not gather data on workplace injuries related to alcohol and drugs. There is no specific law relating to drug-testing and the legality of it depends on the type of work and risks.