Fianna Fáil Senator Brian Ó Domhnaill has been granted leave to apply for a judicial review regarding an investigation by the Standards in Public Office Commission into expenses claims he made while a member of Donegal County Council.
It is understood the investigation is focusing on travel and subsistence claims made by Mr Ó Domhnaill during 2006 and 2007.
The commission was due to begin a public sitting of the investigation on Monday, but this has now been postponed.
The leave for judicial review is based on a request from Mr Ó Domhnaill that the investigation be carried out in Irish and that documents relating to the investigation be made available to him in Irish.
He says his constitutional rights would be infringed if this occurs.
Mr Ó Domhnaill is also refusing to accept documents provided to him by the commission that he says are based on "anonymous allegations".