Hundreds of thousands of teachers will be balloted next week over whether to hold rolling strikes in a bid to make the Government back down over controversial changes to their pensions.
On Tuesday 220,000 of the NUT's teacher members will receive their papers, with 85,000 of the ATL's members receiving theirs next Friday.
All members who belong to or are eligible to join the Teachers' Pension Scheme will be invited to vote, meaning a strike could affect colleges, some newer universities and independent schools as well as academies and maintained schools.
Balloting will continue until 14 June and union bosses will then decide whether to go ahead with the first day of action, which is expected at the end of June.
Further strikes could take place in the autumn term, with the NUT and ATL possibly joined by support-staff union Unison and even heads' unions the NAHT and ASCL.
If both the NUT and ATL vote in favour in the latest ballot, it is expected they will co-ordinate a strike on the same day. Both unions have said they wish to avoid exams.
The NASUWT, which represents a significant proportion of the profession, is yet to announce whether it will hold a ballot. General secretary Chris Keates said she is waiting for the outcome of talks between the TUC and the Government before proceeding.
The ballots come just two weeks after education secretary Michael Gove acknowledged that teachers had an "unspoken contract" with the Government on pensions.
He said that although the Government had accepted the recommendations of the recent Hutton review of public sector pensions in principle, each scheme would be looked at individually.
"We need to make sure that the unique circumstances and the unique commitment that teachers and headteachers give is recognised in whatever reformed system we arrive at," he told the annual conference of the NAHT.
More talks were understood to have taken place this week between unions and the Treasury, and they are expected to continue through the summer term. Union leaders insist that if a satisfactory agreement is reached, they will call off the action.
However, one aspect of the controversial reforms has already come into effect without negotiation - the switch from the Retail Price Index rate of inflation to the lower Consumer Price Index.
The Government has also announced plans to gradually increase contributions by 50 per cent from April 2012.
The overall direction of the dispute is most likely to rest on the potential axing of final salary pension schemes for teachers.
ATL general secretary Mary Bousted told The TES: "Our view is that the negotiations are not producing the answers we want. The Government hasn't responded to any of our warnings that the membership will not be walked over like this."