The Association of School and College Leaders (ASCL) will ballot members on taking industrial action for the first time in its history if ongoing pensions negotiations with the Government fail to bear fruit.
ASCL general secretary Brian Lightman told The TES it was "certain" to hold a ballot if talks fail to lead to a breakthrough, after a survey of its members revealed "strong views" among school leaders.
The announcement follows further discussions between the TUC and the Treasury and a summit of the education unions' general secretaries this week.
The TES understands that, at a meeting called by heads' union the NAHT on Tuesday, leaders of all the main education unions discussed setting up a campaign to increase pressure on the Government - which could include demonstrations and a mass lobby - ahead of a possible fresh wave of co- ordinated strikes in November.
Mr Lightman said no decision had yet been taken on whether ASCL members would be balloted on a full strike, but added that the teaching unions "are all absolutely in agreement about the issue and working together".
He said: "What our survey did reveal was that there were strong views. If (negotiations) fail to work out, then there was certainly considerable support for taking some sort of action.
"What came out very clearly was a strong support from our members for the approach we are taking, and we are doing it that way.
"If the negotiations were to fail, it's quite clear that there is a mandate that we can hold a ballot. I am certain that we will ballot members if there is no resolution."
On Tuesday, chief secretary to the Treasury Danny Alexander said that a "series of constructive meetings" had taken place with the TUC over the pensions reforms.
The proposed reforms would see teachers' contributions rise by 50 per cent, the retirement age rise, and the scheme switch from final salary to career average.
Mr Alexander also offered discussions with individual unions on specific schemes, which would include the teachers' pension scheme, alongside the central talks.
A TUC spokesman said the discussions would allow unions to "fully explore all the issues and to enable unions and their members to reach a judgment on whether agreement is possible or whether more unions will enter into dispute and plan industrial action".
An ASCL spokeswoman said Mr Alexander's statement "outlines some positive progress" in the negotiations, but said members were "ready to challenge the Government if negotiations over pensions do not result in an acceptable deal".
Martin Freedman, head of pay, pensions and conditions at the ATL union, said he feared concessions made to other public sector workers, such as uniformed workers, could lead to teachers being marginalised in the negotiations.
"If concessions are made to other public-sector workers, the room for manoeuvre for teachers will be less."
A joint statement from the NUT, the ATL and the University and College Union said: "Unfortunately there appears to be a real danger that the Government may impose an arbitrary and unfair ceiling on what they are prepared to spend to support teachers' pensions.
"In our view, without real negotiations on this key issue, these talks will be a sham."
Teachers' pension contributions would increase from 6.4 per cent to 9.8 per cent. The ATL has calculated that this would cost the average teacher pound;1,145 a year more, with heads paying pound;1,965 more.
The normal retirement age would go up to 66, and eventually to 68, while the switch from a final-salary scheme to a career-average scheme would hit a teacher's pension package by 15 per cent, unions have calculated.
In his review of public-sector pensions, Lord Hutton also proposed that teachers and heads in independent schools should be excluded from the teachers' pension scheme.
This would affect about 60,000 people.