Thousands of teachers and lecturers are descending on Parliament to protest against planned Government changes to their pensions.
Teaching unions have said they are "united in their determination" to oppose the pension plans.
The unprecedented joint action has been organised by seven unions, who will hand a petition signed by 130,000 people to the Department for Education (DfE). The petition says the Government's proposals are "unjustified", and simply a stealth tax on staff.
Dr Mary Bousted, general secretary of the Association of Teachers and Lecturers (ATL), one of the unions taking part, said: "Teachers and lecturers are united in their anger about the Coalition Government's plans to impose unwarranted cuts to their pensions.
"Over a thousand teachers and lecturers from schools and colleges round the UK are prepared to spend a day of their half-term holiday in London to lobby their MP, and over 130,000 have signed a petition against the cuts, so the Government needs to take notice.
"If the Government is really prepared to negotiate it must be willing to grant some concessions.
"We have always been willing to talk, but we will not be bullied into accepting pension cuts without a fight and members are prepared to take part in a further strike if the Government remains deaf."
The protest is the latest salvo in the bitter row over public sector pensions. Teaching unions argue that the Government's plans will leave them working longer, paying in more, and receiving less when they retire.
And they say the latest action is part of their joint campaign to protest at what they claim is an "unwillingness" by ministers to enter meaningful negotiations and a refusal to carry out a "legally required and overdue" valuation of the Teachers' Pension Scheme.
Ministers have insisted that changes to public sector pensions are necessary to ensure they are sustainable for the future.