Green Party Junior Minister Trevor Sargent will address the Dáil this evening on reports that he made representations to the Gardaí on behalf of a constituent, seeking to intervene in a prosecution.
The constituent was subsequently convicted of threatening and abusive behaviour and fined €500.
Fine Gael has described the letter, which was written on Department of Agriculture headed paper, as "totally inappropriate".
The party's Justice spokesman Charlie Flanagan said if the story is true Mr Sergant will have to resign.
Speaking about the controversy in the Seanad in the last few minutes, Mr Sargent's party colleague Dan Boyle said: "I know he's a decent and honourable man and he'll act accordingly."
Trevor Sargent, Green Party TD for Dublin North, said he approached authorities after a constituent asked for his help over a looming court case.
A spokesman for Mr Sargent confirmed letters had been sent.
“Trevor Sargent made representations on behalf of a constituent who came to him after he was assaulted,” the party official said.
“Having heard the circumstances of the case, Mr Sargent asked the local gardaí to look into the case, particularly as the constituent feared for his personal safety.”
Garda Commissioner Fachtna Murphy has asked senior officers in the north Dublin region to urgently investigate the claims and report back.
Mr Sargent, minister for food and horticulture, is the second Government member to face questions over standards and ethics in public office.
Last week, Limerick TD Willie O’Dea resigned as Defence Minister after making false allegations against a Sinn Féin councillor that he was involved with a brothel and subsequently filed a sworn High Court affidavit denying the slur.