Workplace testing for cannabis, amphetamines and opioids is becoming increasingly common in emergency services, aviation, transport and mining industries.

Employers and unions agree random drug testing is vital for workplace health and safety, but disagree on the most appropriate method.

Last week the Fair Work Commission refused Endeavour Energy's bid to urine test its 2635 employees.

The arbiter had ruled in 2012 that urine analysis was "unjust and unreasonable" because such testing detected drug use from days earlier, while oral fluid testing generally picked up drug taking in the preceding hours. The ruling was upheld on appeal.

Endeavour Energy had argued urine testing could indicate regular, chronic and dependent users of drugs. Urine analysis was also more precise than oral tests, it said.

In September last year Endeavour, with Essential Energy and Ausgrid, suspended saliva testing after the National Association of Testing Authorities declared it was no longer accrediting facilities to perform on-site drug testing of oral fluid.

Endeavour claimed this was "a significant change in circumstances" and asked the Fair Work Commission for permission to introduce urine tests by the end of 2013.

But the tribunal disagreed, finding neither method was infallible, and the testing authority's decision did not mean that on-site oral fluid testing devices were unreliable or that urine analysis was the preferred option.

Electrical Trades Union NSW deputy secretary Neville Betts said the decision "absolutely cements this legal precedent that has wide-ranging ramifications not only for the electricity sector but for every industry that carries out drug and alcohol testing".

Mr Betts said testing should be about identifying potential impairment at work rather than disciplining staff for private actions taken in their own time.

Endeavour Energy's chief executive Vince Graham said the ruling contradicted a November 2011 decision by the commission which endorsed a coalmining employer's right to conduct urine testing. In that case, the commission found urine testing was more accurate.

"Mine workers and electricity workers both work in potentially dangerous conditions and yet different drug testing methods have been ordered by the [Fair Work Commission]," Mr Graham said.

Employment law specialist Adrian Morris from Ashurst lawyers said while there have been a number of decisions by industrial tribunals, there is still no consensus as to what is the most appropriate method of workplace drug testing.

Recently the Fire Brigade Employees Union was successful in its push for firefighters to undergo saliva testing rather than urine testing.

NSW police officers are still required to give a urine sample, in the privacy of a toilet cubicle, when randomly selected.