Tens of thousands of workers are on picket lines across Northern Ireland in one of the biggest strikes in a generation.
Up to 170,000 public sector workers will be taken to the streets overpaid, and health, education, transport and a wide range of civil service services will be severely disrupted.
Fifteen trade unions are taking part in a coordinated action, demanding higher living wages for workers.
In some cases, workers are demanding similar pay to workers in other parts of the UK.
As well as individual pickets, lunchtime rallies will be held in Belfast, Derry, Omagh, Enniskillen and Magherafelt.
In Belfast, six parades will gather at City Hall for a rally at 12pm.
Nurses, teachers, health and education support staff, bus and rail workers and civil servants are among those striking today.
Mark McTaggart, northern secretary of the National Teachers’ Organization of Ireland, told RTÉ’s Today with Clare Byrne that teachers feel “completely undervalued”.
He said teachers have been waiting three years for a pay rise and their salaries have fallen by 25% in “real terms” since 2010.
Mr McTaggart said teachers in Northern Ireland were among the lowest paid in the UK and even lower than teachers in the Republic of Ireland.
The starting salary for a teacher in Northern Ireland is £24,137 (€28,100), while the starting salary for the same teacher in England is £30,000 (€34,932).
Apart from the direct impact on public services, the combination of this industrial action and sub-zero temperatures is expected to lead to widespread national travel disruption.
The road network will be severely hit as only four major routes – the M1, M2, A1 and A4 – will be able to handle the frigid weather due to limited gravel.
Other roads will remain unpaved and people are warned to only make “absolutely necessary” trips.
The Ministry of Infrastructure warned road users that roads leading to limited salt-affected parts of the road network would not be treated and to take extreme caution.
Road users and pedestrians are urged to use extreme caution as gravelling is expected to be disrupted for several days.
Translink bus and rail services were canceled for the day.
Cross-border rail services between Belfast and Dublin are also affected, with limited Enterprise services only running between Dundalk and Dublin.
Schools will be closed and limited medical services will be provided today, as on Christmas Day.
The Ministry of Health said the disruption would be on a scale never seen before in industrial action.
The strike followed a last-ditch attempt to rebuild Stormont.
The Northern Assembly recall failed to elect a council leader after the DUP blocked the election.
The DUP has refused to return to Stormont in protest of post-Brexit trade rules.
The failure to restore power-sharing institutions meant that £3.3bn of policy, including around £600m in public funding, could not be lifted.
Any agreement by Northern Ireland Secretary Chris Heaton-Harris is dependent on the parties returning to Stormont.
Northern Ireland’s political parties, including the DUP and Sinn Féin, are calling for Labour’s money to be released immediately and separated from the broader political landscape.
Unions object to workers’ wages being tied to wider agreements, saying their members are being used as “pawns” and “leverage.”
Ahead of today’s strike, Mr Heaton-Harris said that while civil servant pay would be devolved, a “fair and generous package” had been provided by the UK government to address the issue, including the provision of security for public services. It said it included more than £1 billion for development.
“Ministers need to return to work at Stormont so that governance decisions can be taken this round.”
Cllr Northern said he was “extremely disappointed” that the funding had not been accepted, but said the proposal was still under consideration.
He said: “The time has come for NI parties to make a decision on how to best serve the interests of the people of Northern Ireland.”
The Irish Congress of Trade Unions said the Secretary of State’s strategy had “clearly failed and failed the people of Northern Ireland”.
ICTU Assistant Secretary Jerry Murphy said the strike and rally would demonstrate “industry and public solidarity on a scale never seen before in this location”.
“All that remains is for Chris Heaton-Harris to do the right thing and release the funds,” he said.
Sinn Féin’s Stormont leader Michelle O’Neill said public sector workers went on strike because they felt they had “nowhere else to turn”.
“It’s a very difficult day for public sector workers, but they must go to the picket lines this morning to defend what is reasonable and fair: fair pay and working conditions for public servants,” O’Neill said. I feel that it must be done,” he said. It’s the work they do every day for all of us.
“We deplore the fact that they are forced to the picket line this morning. We deplore the fact that they have had to take this action. But we know that they have no other recourse. I completely understand feeling out of place.”
“I hope that[DUP leader]Geoffrey Donaldson has listened, listened to the plight of workers and made the right decision, even at this late stage, to unite with the rest of us around the executive table. We will support these workers and work to ensure they receive decent wages and conditions. ”
Additional reporting PA