In a report, it is calling on the Government to take action on testing which it claims has doubled, unregulated, in the last decade.
The TUC says its Testing Times report, published in Hazards magazine which it backs, includes evidence that one in eight companies is testing staff for drugs and four out of five bosses would be prepared to test their employees if they felt productivity was at stake.
The 'Testing times' report criticises employer enthusiasm for drug and alcohol testing at work and argues that it is an intrusive and unproven science.
TUC General Secretary Brendan Barber said: 'No-one is suggesting that it is acceptable to be high or drunk at work but staff who may have drink or related problems need help not disciplinary action. A policy for identifying symptoms and a programme for dealing with employee's drug and drink problems is far more effective than random testing.'
The union believes that workplace drug testing is a 'costly waste of time and a gross infringement of an individual's privacy'.
It claims that testing doesn't prove someone's inability to do a job and that: 'All it shows is exposure to a substance maybe months before the test took place'.
A spokesman said: 'While there may be a case for testing in safety critical jobs, tests should never be randomly carried out.
'Every workplace should have a policy on drug and alcohol use drawn up by managers in consultation with union representatives. The policy should state that individual confidentiality will be maintained at all times, with the emphasis on assistance and advice, not disciplinary measures and dismissal.'
Last year, the TUC announced it was mobilising thousands of union members to demand companies make at-work road safety a top priority.
The historic decision was made at the 2002 TUC Congress in Blackpool and has come with a warning that it is time companies take driver safety seriously.
The TUC is the umbrella organisation for more than 70 unions representing seven million workers, and can exert massive influence on UK companies.
The conference heard that the TUC planned to train its 14,000 safety representatives to examine their companies' at- work driving risk assessment strategies, and to force higher standards in safety for fleets.