Teachers today called for an escalation of industrial action, including strikes, amid growing concerns about attacks on pay, pensions, working conditions and job losses.
Delegates at the NASUWT's annual conference in Birmingham today passed a resolution which said that continuing the union's industrial action campaign is "the best means of protecting and safeguarding the interests of teachers and state education until the next general election."
The move raises the possibility of strikes in the autumn term.
The resolution warns that in the face of a "vicious and unjustified assault on teachers, it will be essential to intensify the industrial action campaign".
It says: "Conference is committed to further extending the current national action instructions to restore teachers' professionalism by attacking policies and practices which deprofessionalise teachers, including punitive fallout from the inspection and accountability regimes."
And it endorses the work of the NASUWT's leadership in "setting out the next phase in the Union's industrial action campaign, which will include the escalation of action short of strike action and strike action."
Speaking ahead of the debate, NASUWT general secretary Chris Keates said: "The NASUWT has been in continuous action short of strike since December 2011 in an attempt to get the Government to focus on the real concerns of the profession and realise the effect their attacks are having, not just on teachers and their ability to do their job, but also on children and young people."
She added: "Teachers do not feel there is any area of their working lives the Government has not trampled over and it is impairing their ability to focus on raising standards for pupils.
"If the Government commits to engaging constructively with the NASUWT there should be no need to move to further industrial action but we have reached a point where we feel we have no choice but to take steps to defend teacher professionalism from these attacks."
The NASUWT is the first teaching union today to pass a resolution calling for further industrial action over government reforms.
The National Union of Teachers (NUT), which is meeting for its annual conference in Torquay, is due to discuss a priority motion this afternoon on government changes to public sector pensions.
The motion, which is expected to be heard in private, could pave the way for fresh walkouts as early as this summer.
It instructs the executive to "seek to build a coalition of unions committed to further strike action in the summer term and beyond to defeat the Government's proposals".
And it calls for a discussion with those unions about "all possible forms of joint strike and non-strike action, including national, regional and selective strike action, and campaigning activities such as joint national and local demonstrations and public meetings".
The NUT, along with a number of other trade unions, has been embroiled in a row with the Government over public sector pensions for more than a year.
It took part in a walkout over pensions on June 30 last year, as well as joining the TUC's national day of action on November 30.
NUT members in London also staged a one-day walkout last month.
Earlier this year the NUT, along with some other teaching unions including the University and College Union, declined to accept the Government's latest pensions offer.
Renewed action over the summer term would coincide with the main exams period, when teenagers across the country take qualifications such as GCSEs and A-levels.
The NUT insisted that it was not the union's intention to disrupt exams season.
"Our dispute is with the Secretary of State, and ultimately, with the rest of the Government in terms of public sector pensions," NUT general secretary Christine Blower said.
"We will obviously, when we discuss with other unions, discuss what timing makes sense and which regions make sense, but we would not be setting out, deliberately, to undermine the exams season."
In the past, certain members have been exempted from taking strike action if it affected the exam period.
NUT deputy general secretary Kevin Courtney said the NUT was seeking to work with "as many teaching unions as we possibly can on taking the campaign forward".
"It's absolutely clear that teachers don't accept the changes that the Government is making, and they're only just beginning to see them, so that next month will be the first tranche of the contribution increase," he said.
A Department for Education spokesman said the teachers' pensions deal is "as good as it gets".
"It guarantees teachers one of the best pensions available but keeps a lid on rising costs for the taxpayer," he said.
"We've been in serious talks for months with unions to address their concerns and reach a final settlement. Reforms to public sector pensions are essential - the status quo is not an option."
On Saturday, an NUT poll said that teachers are feeling demoralised and overworked, with concerns that they are facing constant criticism and unrealistic expectations.