The government is set to be prosecuted over radioactive discharges into the River Tamar.
Tritium is produced by reactors on nuclear submarines
The EC says an international treaty is being breached by the UK Government.
But government officials deny the accusation.
The issue is over the release of tritium - a radioactive substance produced by reactors on nuclear submarines.
Levels of the chemical released by Devonport Naval Base increased by 500% last year.
The European Commission says the levels breach the Eurotom Treaty over the release of nuclear waste.
A decision is imminent about whether to prosecute the UK Government.
The levels of tritium increased by 500% last year
But campaigners say, if a prosecution happens, the process could take years.
Ian Avent, chairman of the Plymouth-based Campaign Against Nuclear Storage and Radiation, said: "Whether it can drag on and on, and all the time that is happening, the stuff is being thrown into the environment, or whether it will have a quick resolution I don't know.
"But I do think we should look at other ways of disposing of this nonsense into the environment.
"It's too high a price to pay."
Devonport Management Limited declined to comment, saying the issue was one for the government.
But it did say it believed the treaty did not apply to the defence industry.