The National Union of Workers in Solomon Islands is calling for an immediate independent assessment as to whether cyanide is leaking from the Gold Ridge mine.
Former workers who are union members have provided photographs of what they say is leaking poison.
The accusation is among numerous setbacks the Australian Solomons Gold company has experienced since reviving its operations in the country in 2007.
It maintains in a press release that there is no evidence of leaking cyanide.
But Tony Kagovai, the union's general secretary, says it's putting thousands of lives at risk.
"The security also who went around there have experienced those headaches and all this so it is there, exactly it's there. But I'm surprised they think that there's no leakage in there...they slightly admitted that yes, there's a leakage somewhere, but they lay up to the 18 or so standard...You know that to verify this area you have to have an independent assessor."
Tony Kagovai says the union is awaiting a reply from the Commissioner of Labour as to whether such an assessment will be conducted.