Clear guidance is needed from the Government on drug testing in the workplace to clear up "confusion" over the legality of random or routine checks, union leaders said.
The TUC said proper policies should be in place for dealing with drug and alcohol abuse in industry, claiming that some employers could be using random drug testing to try to get rid of staff without paying redundancy.
TUC general secretary Brendan Barber said: "Clearly no employer can ignore drugs use in the workplace. Individuals who come to work under the influence of any kind of performance-influencing drug may not only be risking their own safety but also that of others around them."
He added: "But the way to tackle this danger is by having proper policies in place for dealing with drug and alcohol abuse in the workplace, rather than introducing random testing which is not only a breach of a person's right to privacy and dignity, but also of dubious legality.
"Levels of testing in the UK may still be well below those in the USA, but many employers are being seduced by the marketing campaigns of drug-testing companies into seeing random testing as the solution to sickness absence problems. This is why the Government needs to produce clear and definitive guidance on testing, especially on the legal issues."
Firms should develop drugs and alcohol policies which support staff rather than resorting to drug testing, said the TUC, which published a new guide on the issue for union safety reps on Thursday.