The scandal broke out on Wednesday when the Zagreb-based Vecernji List daily published transcripts showing that a Slovenian arbitrator and a Slovenian diplomat had discussed the case and lobbied other judges sitting on the tribunal to influence the outcome of the arbitration in Slovenia's favour.
The Slovenian member of the Arbitral Tribunal, Jernej Sekolec, and the authorised Slovenian government representative, Simona Drenik, have resigned in the meantime, and the tribunal has said it will resume the proceedings once his position has been filled.
The Croatian government believes that this was a formal, "technical" response to the situation when the tribunal is left without an arbitrator, but that the tribunal failed to address the gist of the matter. That's why it sent a letter to the tribunal on Friday to explain the latest developments, providing links to the recordings and transcripts of telephone calls between the Slovenian officials.
Croatia believes that the Arbitral Tribunal should dissolve itself because it has been so compromised by the scandal that its ruling cannot be accepted as legal.
The source said that the tribunal had "little time to act" and that the government expected a response before an extraordinary session of the Croatian parliament, which has been requested by the government and several parliamentary parties. The session has been set for Wednesday.
The European Commission had mediated the arbitration agreement between Croatia and Slovenia in 2009, which unblocked Croatia's EU accession negotiation.