The DUP has pledged to resist a plan by campaigners for the so-called Colombia Three to bring their case to the European Union.
Sinn Féin Assembly member Ms Caitríona Ruane, who, with party colleague Mr Gerry Kelly, is in Bogota consulting with Colombian lawyers about the 17-years prison terms imposed by the Colombian courts on the three men, said she would be seeking the support of the EU.
The DUP MEP, Mr Jim Allister, however, responded by launching what he termed a "counter-offensive in Europe" against attempts to enlist EU support for the men.
Mr Allister has written to the President of the European Commission, Mr José Manuel Barroso, urging him to support the DUP campaign to have the three men - Niall Connolly, James Monaghan and Martin McCauley - brought "to justice".
Mr Allister has already spoken in the European Parliament on the IRA's alleged involvement in Colombia , and e-mailed every MEP with information supporting this claim. He has also written in similar terms to the British Foreign Secretary, Mr Jack Straw, to urge him to ensure the European Union is "not engaged on behalf of terrorism".
In his letter to Mr Barroso he wrote: "No amount of Sinn Féin propaganda can conceal the reality that their activists were plainly engaged in assisting the drug-funded Marxist guerrillas of FARC."
