Delegates at the National Union of Teachers (NUT) national conference in Torquay vowed to stand fast against government scavengers circling their pensions today.
NUT general secretary Christine Blower told reporters that the union had decided to seek "unity with other unions" for industrial action over the summer.
"Our campaign has been built on the strength of our membership, who have played a magnificent role in defending teachers' pensions and fair pensions for all - particularly through the national strikes on June 30 and November 30 and the London strike of March 28," she said.
The union's executive would continue a "principled and determined campaign" in the months to come, she added.
The long-awaited motion came more than three months after the union's executive voted to reject the government's final offer and a fortnight after 6,000 London members held a one-day regional strike.
Delegates voted to hold the debate in secret but sources said many members had wanted an explicit stance on national strikes.
One failed amendment called for a one-day national strike on May 10 alongside public-sector workers in PCS and Unite, while another called for week-long national strikes in May and June. A call for a fortnight of rolling regional strikes was ruled out of order.
One speaker described his local members as "mystified and angry."
London officers had worked hard to organise March's regional strike, he said but members wanted more than one-day events months apart. It would be good to have the other teachers' unions on board, but it should be a matter of principle to go it alone if necessary, he added.
Several delegates who did not wish to be named said their members were losing heart as rolling regional strikes did not make the headlines and sometimes did not even reach union members elsewhere in the country.
But another delegate who did not wish to be named insisted any strike action needed to be "sustainable."
Continued strikes would hit members' pay packets hard, they said.
The decision came just hours after fellow teachers' union NASUWT declared their own return to the picket lines, with delegates voting to immediately escalate industrial action up to and including strikes.
But a Department for Education spokesman insisted the government would not budge.
The deal tabled in December was as good as it got, he said.
The offer as it stands would see a rise of up to 50 per cent in weekly pension contributions despite a two-year pay freeze, a rise in the retirement age from 66 to 68 and reduced payouts based on a career average.
Concessions so far include exemptions for staff retiring in the next 10 years and a one-year exemption for workers on less than £26,000 a year.
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