Claims that bogus drug tests are being used by firms to make redundancies have been described by one organisation as "disturbing".
Release, a national centre of expertise on drugs and drugs law, reported that it took 145 calls to its helpline concerning drug testing at work during the first quarter of this year.
This compares with a total of 31 such calls during the same period in 2008.
Responding to the figures, general secretary of the Trades Union Congress Brendan Barber said: "The suggestion that spurious and arbitrary drug tests are being used for dealing with redundancies is deeply disturbing.
"Employers should have clear and transparent policies on redundancy, known to workers and negotiated with unions if possible."
He added that policies on drug use should also be clear to staff and any testing for drugs should be limited in use, proportionate and accompanied by access to counselling and welfare programmes.