Activists from the environmental group Greenpeace are arriving in Dublin this week to prepare for a protest against a shipment of radioactive waste which will travel through the Irish Sea to Sellafield.
The group's boat, the Rainbow Warrior, is set to dock in Dublin, from where campaigners will plan their strategy.
The material, claimed by some to be enough to create 50 nuclear bombs, is being sent back from Japan after the authorities there refused to accept it from the Cumbrian nuclear waste processing plant.
A number of Irish politicians have protested about the radioactive material passing within miles of the coast.
Greenpeace has vowed a peaceful protest and the Rainbow Warrior will be among a flotilla expected to greet the two cargo vessels when they arrive in the middle of next month.
The Labour Party marine spokesman, Mr Eamon Gilmore, has called on the Minister responsible for marine affairs, Mr Ahern, to "use every international convention on marine safety to prevent this shipment from travelling through the Irish Sea".
He said: "The Minister must assert Ireland's rights to protect its citizens from dangerous shipments in neighbouring waters, and prevent this shipment, which contains enough material to make up to 50 nuclear weapons."
The Japanese authorities demanded the waste be shipped back to Sellafield after it arrived in their waters in 1999 amid the revelation that safety records at the Cumbrian facility had been falsified.
A spokesman for British Nuclear Fuels Ltd (BNFL), which operates Sellafield, said: "These transports are safe and secure. The standards that we meet are laid down by the International Maritime Organisation."
He added: "It is not weapons-grade material. People would find it almost impossible to separate the material out to make any form of nuclear device."