Heads say they have "run out of patience" after their attempt to achieve what they regard as fair representation was thrown out at a meeting of the teachers' panel earlier this month.
They are demanding that the Educational Institute of Scotland drop two of its eight seats to allow primary and secondary heads' voices to be heard at national level.
Bill Milligan, president of the Association of Head Teachers in Scotland and the head of Dalmilling primary in Ayr, said: "It looks as if we're heading for a judicial review as we have very strong Queen's Counsel opinion that this is unfair practice under European law."
The EIS controls the 11-strong teachers' side of the negotiating committee with eight seats, leaving the Scottish Secondary Teachers' Association with two and the Professional Association of Teachers and the National Association of Schoolmasters Union of Women Teachers sharing a place in rotation.
The AHTS and the Headteachers' Association of Scotland, the secondary heads' union, are two of the listed bodies from which the teachers' side draws representatives, but the membership tally rules them out from a place at the negotiating table. Both are present on the teachers' panel prior to the full negotiating committee with representatives of councils and the Scottish Executive.
Mr Milligan says that the EIS would retain its firm grasp even it conceded seats. "Even with headteacher representation, there's no way we could outvote anybody. It's simply a matter of the voice being heard. I would see headteachers being on any side that advantages children," he continued.
Local authority bosses meeting in Dunfermline last week (page 3), suggested heads taking a place on the management side at local level, but Mr Milligan points out it was Sam Galbraith, the former Education Minister, who placed them firmly on the union side. "We're following that through. As for headteachers acting as advisers to local authorities, you would expect that to happen any way," Mr Milligan added.
Ronnie Smith, general secretary of the EIS, said that the AHTS is represented on the larger teachers' panel from which the negotiators are selected and is entitled to put its views.
The association represents just 2 per cent of the group represented by the panel, Mr Smith added.
Leader, page 10