Teachers could go on strike for the first time in more than a decade next term unless David Blunkett drops plans for performance-related pay.
A motion at this weekend's National Union of Teachers' annual conference in Brighton - just hours after the Education and Employment Secretary addresses delegates - would authorise a ballot for industrial action, including immediate non co-operation with teachers' appraisal and a one-day summer-term strike.
The NUT's programme of stoppages during the pay campaign of the mid-l980s was its last nationwide action. The whole union last went on strike together in 1969.
Mr Blunkett is unlikely to have to seek refuge in a cupboard from militants on Saturday - as he did four years ago in Blackpool - but he can expect a tough reception.
The teaching Green Paper, to which the NUT filed a highly critical response to the Government this week, has united members in opposition and is certain to dominate the conference.
"Mr Blunkett, his ministers and the Prime Minister have continued to denigrate the profession and talk the language of failure. You can't do that and expect applause," NUT general secretary Doug McAvoy said this week.
"The Government has a period of time to reassure teachers. If it goes down the road of imposition, it will trigger action."
This is the first conference where Labour's actions can be examined alongside its policies. Last year, literacy hours and action zones were still only plans; this year they are reality. Speakers are expected to detail the problems they have putting the literacy strategy into practice. The debate on action zones will be less united.
Mr McAvoy's verdict is mixed. Policies teachers favour - like extra funding and smaller classes - have yet to work through to the classroom. Others, like the continuing support for the chief inspector of schools, provoke hostility. Labour's big problem though is its failure to work in partnership.
"I don't think the Government believes in it," Mr McAvoy said. "It announces things for which there has been no prior consultation or even warning."
His tough line on the Government is not, he said, an attempt to appease the NUT's left-wing before June's leadership election when he faces a challenge from former union president Christine Blower. He would have opposed the Green Paper at any time.
If he wins the election, Mr McAvoy hopes to see moves at long last towards a single teacher's union - the traditional motion calling for it appears at the conference again this year.
Only the second largest union, the NASUWT, can delay it, he said - and the next few years will see all three classroom leaders retire, allowing a fresh start.
"I think the pressure on schools will build up for a single organisation - and in some ways the Green Paper will hasten that."