The company carrying weapons-grade plutonium from the United States to Cherbourg in France is to seek an injunction today to stop protesters interfering with the shipment.
The case is being taken by Pacific Nuclear Transport Limited and French nuclear energy firm Areva, and is due to be heard today.
A spokesman for British Nuclear Fuels Ltd, which is the main shareholder of PNTL, told ireland.comthe injunction was being sought to allow the shipment to dock safely and was not about "interfering with anyone's right to protest".
For security reasons, the spokesman could not say when the shipment was due to arrive in Cherbourg. It is believed that breaching the injunction would incur a fine of €150,000.
The Government has sent the Coast Guard and the Air Corps to ensure the ships carrying the plutonium do not pass through Irish territorial waters, although it does not know the ships' location.
The shipment, which is en route from the US port of Charleston, is believed to have passed within 150 miles of the Irish coast in recent days.
A spokesman from the Department of the Environment said the Government had received assurances from the US and France that the two vessels would remain in international waters.
"The Coast Guard and the Air Corps have been dispatched, but we have no reason to believe that the assurances [about not passing through Irish waters] we have had are false. There isn't any reason to go through Irish waters to get from the US to France."
The Government had not been given the co-ordinates of the ships, he said, and did not know when they would be at their nearest point to Irish shores.