Tony Blair has flown home a day early from holiday in Florida to try to rescue hopes of devolution returning to Northern Ireland by the end of March.
Tony Blair is returning home from holiday early for talks
Sinn Fein's leadership voted last month to hold a conference on the issue of whether to support policing.
But the party has now signalled this is in doubt because the move had not received a "positive enough" response from DUP leader Ian Paisley.
If the conference does not go ahead, the March election may be in doubt.
Although Mr Blair has been away on his Christmas and New Year break, he has also been involved in intensive discussions with Northern Ireland politicians.
More than two-thirds of Sinn Fein's executive last week voted in favour of holding a conference on the issue of supporting policing.
Policing has been a dividing issue between the DUP and Sinn Fein
Party leader Gerry Adams said the meeting would be held, but only if the two governments and the DUP gave a positive response.
In his new year message, DUP leader Ian Paisley said Sinn Fein's "begrudging movement" on policing reduced the prospect of any immediate action towards restoring devolution.
However, Mr Paisley said his party would "not be found wanting" if Sinn Fein honoured its commitment "with actions".
BBC Northern Ireland political correspondent Gareth Gordon said it seemed that these comments were "not positive enough for Sinn Fein".
If Sinn Fein's ard fheis on policing does not happen by the end of January, the 7 March assembly and planned return of devolution three weeks later would also be in serious doubt.
DUP MP Nigel Dodds said that as yet, there was nothing tangible to which his party could respond.
"Instead of whinging and running to Tony Blair, Sinn Fein should get on with doing what it is supposed to do," he said.
SDLP leader Mark Durkan said it was important that Sinn Fein made its own decision on signing up to policing.
"If Sinn Fein are satisfied that changes in terms of policing are being delivered by the Policing Board and all the work that has gone on there, they should make their move on policing in terms that they are in control of," he said.
Ulster Unionist leader Sir Reg Empey blamed the current situation on side deals between the DUP, Sinn Fein and the British government.
"I think what we're seeing with Blair flying home is almost a repeat performance of 24 November when a piece of choreography that had been cobbled together over the holidays went wrong.
"This spells out what is wrong with this whole debate over policing - it's been done as part of a series of side deals behind the scenes."