One diplomat, speaking on condition of anonymity, said that the EU's reasoning for designating the MKO will be posted in its official journal.
The European Union will send letters to groups and individuals on its terror register to explain why they are listed, EU diplomats said Friday.
The decision, to be adopted Monday by EU foreign ministers, was made in the wake of a ruling last year by Europe's second-highest court annulling a freeze on the assets of the main Iranian opposition group in exile.
The Court of First Instance ruled that the EU had not respected the right to a fair hearing of the People's Mujahedeen of Iran (OMPI), when it ordered the asset freeze in May 2002.
One diplomat, speaking on condition of anonymity, said that the EU's reasoning will be posted in its official journal for the groups and individuals for whom it has no address.
Those listed have 30 days "to present their arguments" against the decision.
The terror register lists more than 50 organisations and individuals, including the armed Basque separatist group ETA, Sri Lanka's Tamil Tigers and the Islamist group Hamas.
It is supposed to be revised every six months but this has not happened because of uncertainty caused by the court ruling.
An asset freeze is imposed on those who figure on the list.
The EU has already written to OMPI, recalling "the organisation's past, notably the attacks that it has been responsible for", the diplomat said.
Iranian Interior Minister Abdolreza Rahmani Fazli called for tougher measures against the Mojahedin-e Khalq Organization (MKO, also known as the MEK, PMOI and NCRI) terrorist group by the European Union...