The Transport Workers Union wants police to investigate trucking companies after a drug testing blitz on drivers.

Fourteen truck drivers tested positive to amphetamines or cannabis during a police operation at a major truck testing spot near Goulburn last week.

National secretary Tony Sheldon says drivers are resorting to taking drugs to stay awake and meet the heavy demands of their employers.

Mr Sheldon says New South Wales Police need to target the companies.

"Targeting the driver is like getting the tail of the lion," he said.

"It's the head of the beast that makes all the decisions, that's the clients, the ones that actually make the economic advantage out of having sweatshops on wheels."