In the first three months of 2009, Release took 548 calls, of which 145 (26%) involved drug testing at work. This compares with 493 calls in the same period last year, of which 31 (6%) related to this issue.
The calls mostly came from employees concerned about drug testing because their employer had not subjected them to the practice before - even though in many cases they had been in the job for many years.
Sebastian Saville, executive director of Release, said: "This is a worrying practice that may well breach employees' human rights and their rights to privacy.
"Employers risk alienating staff by forcing them into intrusive tests and should be supporting any staff who might be experiencing drug problems, not using it as an excuse to make cheap redundancies."
Work place drug testing increases five-fold in a year
Drugs helpline Release has reported a fivefold increase in calls about drug testing at work, prompting fears that firms are looking for excuses to make "cheap redundancies".
