A meeting is being held in Plymouth on Thursday to discuss concerns about nuclear work which is carried out at the city's dockyard.
Tritium is released from submarine reactors
It will be addressed by former Environment Minister Michael Meacher.
The main issue is over the release of tritium, a radioactive substance produced by reactors from nuclear submarines based at the Devonport yard.
Levels of the chemical released by Devonport increased by 500% last year.
The European Commission says that breaches the Euratom treaty over the release of nuclear waste and that a decision is imminent about whether to prosecute the government.
The Campaign Against Nuclear Storage and Radiation in Plymouth (Cansar) says if that happens, the process could take years.
However, the government has said the regulations do not apply to the dockyard because it is a military site.
It has also said that even the higher levels tritium discharges at Devonport remained well within national and international guidelines and was well below that produced by naturally occurring sources in the area.
Mr Meacher has said permission to discharge radioactive substances into the River Tamar could still be altered.
He said: "The ministers who did give their approval a year or two ago have said their approval can be modified later."
Devonport is home to the Royal Navy's seven Trafalgar-class nuclear-powered submarines and has four decommissioned nuclear submarines awaiting dismantling.
The meeting is being held at the Guildhall in Plymouth at 1930 GMT.