The TUC said the company involved in the Glasgow factory blast on 11 May was served with a Health & Safety Executive (HSE) improvement notice in February 2000.
It said the notice was served for failing to maintain adequate risk assessments on hazardous substances.
The Scottish TUC has written to the HSE seeking clarification on health and safety enforcement activity at the factory.
STUC health and safety officer Ian Tasker said: “This is the worst industrial accident in the past 25 years and the STUC considers it a duty, both to workers in this factory and throughout Scotland, to work to ensure that health and safety procedures and enforcement minimise risks at all times.”
Scotland's first minister Jack McConnell has promised a full and thorough inquiry into the blast, which left nine people dead and 17 seriously injured.
