Teachers, nurses, bus and train drivers, police staff and civil servants are among up to 170,000 public sector workers walking out in Northern Ireland in one of the largest strikes ever seen in the province.
Northern Ireland will largely grind to a halt as the workers, from 16 different unions, take to picket lines in protest at pay and conditions.
Parades and rallies will take place across the region including in towns and cities such as Belfast, Derry/Londonderry, Enniskillen and Omagh.
Schools will be shut, buses and trains will be cancelled and a greatly reduced health service will operate, with all but emergency procedures likely to be cancelled.
With sub-zero temperatures across Northern Ireland, there will be no gritting of almost all non-motorway roads, and drivers are being warned not to drive unless absolutely necessary.
Secretary of State Chris Heaton-Harris said strikes will be "disruptive for people across Northern Ireland".
So, what's behind this huge level of disruption?
Unions say the wage increases received by their counterparts elsewhere in the UK in recent years have not been matched in Northern Ireland - and the statistics seem to bear that out.
For example, the starting salary for a teacher in NI is £24,137, far behind the £32,317 wage in Scotland, with salaries of £30,742 in Wales and £30,000 in England.
Pay for nurses and civil servants similarly lag behind the rest of the UK.
Of course, Northern Ireland's dysfunctional political landscape is copping most of the blame.
Wednesday saw the seventh failed attempt to restore the Assembly and Executive at Stormont as the Democratic Unionist Party (DUP) stubbornly refuses to participate over its post-Brexit trading concerns.
In the absence of the devolved government - gone almost two years - departments say they can't make new pay offers.
The UK government - in the form of Mr Heaton-Harris - has dangled a £3.3bn carrot for the parties to get back to work at Stormont, including almost £600m to resolve pay claims.
But he says he doesn't have the power to release the funds without the Executive returning - a claim many angry workers simply don't believe.
"I am deeply disappointed that the significant funding offer from the UK government to address such issues has not been taken up," he said.
"This package has been on the table since before Christmas and will remain there, available on day one for an incoming Northern Ireland Executive."
There is huge frustration at both local and national politicians here; and that will be manifested at freezing picket lines in what's being billed as the biggest strike in Northern Ireland's history.