Nationalist leader John Swinney has called on First Minister Jack McConnell to investigate claims that a nuclear plant in England is polluting the Scottish coastline.
There have been claims about pollution from Sellafield
Mr Swinney spoke out after a meeting in Dublin with the Irish environment minister Martin Cullen and members of the Irish Parliament campaigning to have the Sellafield plant in Cumbria shut down.
The campaigners claim nuclear waste from the facility has contaminated both the Irish and Scottish coastlines.
The Scottish National Party's Mr Swinney said it was time for a full-scale investigation into the matter.
And he said Mr McConnell should announce plans to monitor the level of radioactive pollution in Scottish waters.
He said: "At present, the only monitoring that is conducted is in the immediate vicinity of Scottish nuclear plants.
"The reality however is that pollution from Sellafield has spread right round our coastline.
"Until we have an accurate picture of the extent of the contamination, we do not even know how much damage is being done.
"As a first step, I am calling on Jack McConnell to instigate a full scale investigation into the extent of Sellafield's pollution of Scottish waters.
"This will provide the hard evidence that could prove vital in the campaign to see the plant shut."
The SNP leader added: "The Scottish Executive must put the protection of our environment before loyalty to their London masters.
"Sellafield is poisoning our seas. It's time the Executive stood up and fought for Scotland."
A spokesman for the executive said the Scottish Environment Protection Agency (Sepa) monitored the impact of discharges from nuclear sites in Scotland, Sellafield and elsewhere.
He said this had shown discharge levels in Scotland were "well beneath internationally-accepted limits".
"Sepa is currently carrying out a comprehensive review of the monitoring programme," he added.
"While discharges from Sellafield are a matter for the environment agency, Sepa is routinely consulted to ensure adequate protection of the people and the environment of Scotland."