Speaking at the National Ploughing Championships in New Ross, he defended his decision to write the letter. He said he was entitled to write it.
He had earlier been urged to make a full statement over his apparent intervention in a housing allocation case to prevent a Traveller family from being housed.
The Irish Traveller Movement has expressed concern.
It said it understands that neither Minister Hogan nor Junior Minister Jan O’Sullivan have the legislative functions to impose or intervene in individual cases on accommodation matters.
“We are therefore concerned that in this case involving a family in Kilkenny that Minister Hogan should appear to intervene favourably on a constituent’s behalf, in what could be interpreted as being opposed to the favourable provision of housing to Travellers.”
Ms McDonald held up a copy of the Irish Daily Mail, where the story first appeared, saying Mr Hogan needed to be made aware that discrimination was illegal, including discrimination against Travellers.
Fianna Fáil’s Éamon Ó Cuív said at face value it was a very serious issue.
He said that a minister interfering in a housing allocation process to prevent a Traveller family being housed on the basis of them being Travellers would be “an extraordinary abuse of power”, as well as being illegal.
Speaking on RTÉ’s News at One, Mr Ó Cuív called for Minister Hogan to publish the reference that he made to Kilkenny County Council.