Northern Ireland Secretary Chris Heaton-Harris has been urged to intervene as the region prepares for what is expected to be one of the biggest public sector strikes in recent history.
It will come next week after teachers, health workers, transport workers and civil servants took part in previous walkouts over an outstanding pay award.
Unions across sectors will take part in the “day of action” on January 18 in response to the failure to award a pay deal in line with colleagues across the UK.
On Monday morning, major teachers union, the NASUWT, confirmed it will join the strike.
Dr Patrick Roach, NASUWT general secretary, described the pay situation for teachers and lecturers in Northern Ireland as “desperate”.
“Teachers have not had a pay increase for three years while FE lecturer pay is even worse again. Our members shouldn’t be in the position where they must take industrial action to get the same basic rates of pay as colleagues elsewhere in the UK,” he said.
During talks between Mr Heaton-Harris and the Stormont parties in December, a £3.3 billion financial package to accompany the return of devolution was offered.
The package would include money to make an outstanding pay award to public sector workers. However with Stormont remaining effectively collapsed that funding has not materialised.
An NIO spokesperson said the package will remain on the table until a new Executive is formed to allocate it.
Dr Roach added: “Given that the Secretary of State has identified £584 million to address public sector pay issues as part of a financial package for the return of a Northern Ireland Executive, it is scandalous that our members have been left with no other option than to take strike action to highlight the dire situation that they face.”
Sinn Fein MLA Conor Murphy said public services are “on their knees”.
He told reporters at Stormont earlier that the January 18 strike will be “probably one of the biggest ever seen here” to secure “fair pay”.
SDLP leader Colum Eastwood urged Mr Heaton-Harris to intervene ahead of the strike.
“There are only 10 days left for an urgent intervention to address the needs of public sector workers ahead of a day of generalised action next Thursday,” he said.
“Nurses, teachers, civil servants and other public sector workers aren’t taking this action lightly – they’re giving up a day’s pay and going out on strike to put down a marker for this government and for political parties here.
“The needs of workers have been overlooked, or used as part of some shameless blame game for far too long. I have written to the Secretary of State today urging him to take decisive action to deliver the pay awards that workers deserve and that the Northern Ireland Office and British Treasury have already agreed to fund.
“Any political leader, whether it’s Chris Heaton Harris or Jeffrey Donaldson, should be ashamed that nurses, teachers and other public sector workers will again be forced to take strike action for pay justice while those with the power to deliver it sit on their hands. It is indefensible and their approach must change.”
A Northern Ireland Office spokesperson said: “The Secretary of State has expressed his disappointment that a new Executive was not up and running to take the offer on the table and deliver it for the people of Northern Ireland before Christmas.
“The fair and generous package offered by the UK Government is worth over £3 billion, including up to £584 million to address public sector pay, and more than £1 billion to stabilise Northern Ireland’s public services.
“However, this package is on the table and will remain there, available on day one of an incoming Northern Ireland Executive to take up.
“It is now for the NI parties to come together, restore the Executive and begin to address the challenges facing the people of Northern Ireland, including public sector pay.”