The number of workplace related deaths could be up to 10 times higher than reported by the Health and Safety Authority (HSA), according to Siptu.
The HSA's annual report for 2004 shows that 50 people died as a result of occupational accidents.
There were 23 workplace fatalities in the first five months of 2005.
However, Siptu estimates that the actual number of deaths caused in or by work could be an average of 500 a year - 10 times the number that are reported and investigated.
"Because the Health and Safety Authority only collects data on the number of illnesses or injuries occurring in the workplace, their figures do not reflect the true level of workplace fatalities," Siptu health and safety officer Sylvester Cronin said.
Deaths which occur due to long-term illnesses and diseases directly related to workplace conditions are not listed in the annual HSA figures.
While these statistics can be difficult to compile, the number of working drivers killed in road accidents could easily be collated, but are also absent from the figures, he said.
"There is evidence that up to one-third of all road accidents are work related and with a broad average of 360 fatalities a year, 120 of these are likely to be work related."
Between 4 and 8 per cent of cancer deaths are work related, largely due to exposure to chemicals, dust and other air pollutants, he said.
"An average of seven and a half thousand people die each year from cancer related illnesses, Mr Cronin said.
"Even taking the lower figures of 4 per cent, it would be fair to say that 300 of these deaths were work related."
Similar figures were expected for cardiovascular and respiratory illnesses contracted in the workplace, he said.
Siptu is calling on the Government to establish a scientific review body to examine and collate fatal workplace injuries and illnesses.
"We need to be able to properly size the problem so we can fully addresses it. The Government response is always a reflection of the size of the problem," Mr Cronin said.
