Senator Norris is expected to win support at a special meeting of Cork County Council at 11am on Tuesday, before a number of other councils vote on which candidate to nominate.
Nominations close on Wednesday, with Senator Norris and Ms Scallon both likely to still need support from four more councils each as an alternative to the Oireachtas support route.
Cork county councillors were told of the change of plan via a formal letter from County Mayor Tim Lombard which was couriered to their homes late last night.
The special meeting was requested by Independent councillor David Boyle.
While 13 councillors must normally request a special meeting, Mr Lombard — a Fine Gael official — has taken advantage of a rule allowing a mayor to push through the call.
The move came after Taoiseach Enda Kenny said his party colleagues should not block more people entering the race.
Mr Lombard said he was not aware of Mr Kenny’s comments and that he simply “didn’t want to stand in the way of democracy”.
Cork County Council is made up of 21 Fine Gael councillors, 11 Fianna Fáil, seven Labour, seven Independents and one Sinn Féin councillor.
The news emerged as Senator Norris and Ms Scallon edged closer to joining the packed presidential race. South Dublin and Laois local authorities will meet on Monday, and Cork County and Dublin City on Tuesday to consider motions supporting Mr Norris. Cavan, Westmeath, Longford and Donegal will meet early next week over support for Ms Scallon.
Carlow, Roscommon and Waterford City will also decide, while Kilkenny will not make a decision until Wednesday.
An online Millward Brown Lansdowne opinion poll has put David Norris ahead in the race, should he enter, on 27%.
Labour’s Michael D Higgins is on 18%, Sinn Féin’s Martin McGuinness on 15%, Independents Mary Davis and Sean Gallagher on 15% and 11%, Gay Mitchell on 11%, and Independent Dana Rosemary Scallon on 4%.
Independent TD Michael Lowry and Fianna Fáil’s Mattie McGrath are the last remaining Oireachtas members yet to decide their vote.
Meanwhile, Fine Gael Justice Minister Alan Shatter said Martin McGuinness’s failure to embrace Queen Elizabeth II’s recent visit here showed he was not an appropriate person to represent the state.