Lawyers for Sinn Féin have written to the Attorney General seeking advance copies of the information being sent to homes about the EU Fiscal Treaty.
Sinn Féin is also threatening legal action over a Government website which had featured material promoting a 'Yes' vote in the referendum.
Under legal rules, public money cannot be spent promoting only one side of the argument.
This afternoon speeches by the Taoiseach Enda Kenny, Tánaiste Eamin Gilmore and Minister for European Affairs, promoting a 'Yes' vote were withdrawn from the website.