By Sean Coughlan
BBC News education correspondent, in Birmingham
With an election imminent, teachers are setting out the policy battle lines
A teachers' union has called on its members to "defend state education", saying there is a stark choice between public services and a free market.
A motion at the NASUWT conference in Birmingham has backed industrial action in support of public service values.
It will be seen as an attack on Conservative plans for "free schools".
Tory schools spokesman, Michael Gove, told the union that allowing more providers to run schools would widen opportunities in poorer areas.
In the run up to the calling of the general election, the NASUWT union is setting out the battle lines over schools policy.
The motion backed by delegates on Sunday says there is a "stark choice between those who are committed to the values and ethos of public services and those who cling to the wreckage of the failed free market philosophy".
This will be seen as a criticism of Conservative free school plans to allow parents and other groups to have public funds to set up schools.
Speaking ahead of the debate, the union's general secretary Chris Keates labelled the plans as being "beyond rational thought" and a "major threat to the state system".
She said the policy was designed to "dismantle state education" - and claimed that it would mean schools being set up above shops or in office blocks.
The Conservatives have argued that the policy will offer extra choice to parents, rather than diminishing what is already available.
Speaking at the conference on Saturday, Mr Gove challenged the teachers' union to set up their own school - to show how their principles would work in practice.
The conference will hear warnings from the union's leadership that a "decade of unprecedented investment" in schools must not be "eroded".
The motion on defending public services also accused "serial detractors of public services" of using public spending pressures as an excuse to "butcher public services".
The conference had already voted in support of industrial action against any attempt to change public sector pensions.
Protests against "privatisation" in schools - both the Tory's free schools plan and the government's academy programme - have also been raised at the annual conference of the National Union of Teachers in Liverpool.
Douglas Morgan from Birmingham said the NUT needed to put itself "on a war footing".
"This is about the privatisation of education at a time when the government wants to give money to big business," he said.