Scotland is set to face an even bigger teaching strike next month as another union announced it would join walkouts.
Teachers from two other professional bodies were already planning to strike across the same two days in Scotland.
“The Scottish government and employers will need to bring forward a substantially improved pay offer if they want to see an end to this dispute,” Dr Patrick Roach, the NASUWT general secretary, said.
“Any disruption caused by this further strike action is their responsibility.”
It comes as the UK faces other winter strikes from NHS and rail workers, as well as airport and Border Force staff.
Three of Scotland’s most remote airports closed on Monday due to strikes. Meanwhile nurses in England, Wales and Northern Ireland will walk out again on Tuesday, while ambulance workers will strike on Wednesday in England and Wales.
Train passengers have also been told to brace for disruption over the Christmas period due to strikes, with thousands of Network Rail workers to walkout from 6pm on Christmas Eve until 6am on 27 December.
In Scotland, members of the Educational Institute of Scotland (EIS) members will walk out on 10 and 11 January, as well as Scottish Secondary Teachers’ Association (SSTA) members on the second day.
NASUWT announced on Monday it would launch strikes in primary schools on 10 January and in secondary schools the following day.
The union is calling for a fully funded 12 per cent pay award for 2022/23 and said that the current pay offer tabled by ministers and Cosla amounts to a further real-terms pay cut.
Dr Roach said: “We have been left with no choice but to call two further days of national strike action as a result of the failure of ministers and Cosla to offer an improved pay offer.
“At a time when teachers are facing the biggest squeeze on their finances in a generation, offering what amounts to a further real-terms pay cut is simply not good enough.
“Our members are not prepared to stand by while their pay dwindles and their living costs rise.
“The government and employers will need to bring forward a substantially improved pay offer if they want to see an end to this dispute.”
Teachers have already rejected a deal which would see most staff in classrooms receive a 5 per cent pay rise, although the lowest earning teachers would get a 6.85 per cent increase.
Mike Corbett, NASUWT national official Scotland, said: “Members are determined to continue with our campaign of industrial action and will stand together with teachers in other unions to send a united message to the Scottish government and employers that they deserve a fair pay settlement.
The Scottish education secretary Shirley-Anne Somerville said: “We remain committed to a fair, sustainable settlement for Scotland’s teachers and will continue to engage with teaching unions and Cosla constructively.
“It is very disappointing that the teaching unions have rejected the latest offer – the fourth of which has been put to unions – which mirrors the deal accepted by other local government workers.
“The request for a 10 per cent increase from the teacher unions collectively in Scotland is not affordable within the Scottish Government’s fixed budget.”
SSTA and NASUWT members took two days of strike action earlier this month while EIS members walked out on 24 November.
Katie Hagmann from Cosla, which represents local government in Scotland, said: “We are disappointed that strikes are going ahead.
“In an effort to prevent strikes happening, we as employers made a revised fourth offer to our trade union colleagues, that did include additional money. It was a fair and affordable offer which recognises the cost-of-living crisis as the priority by focusing on higher increases for staff on lower pay points.”
She said the offer was in line with others made to public sector workers.
Additional reporting by Press Association