The gulf between the two largest unions widened this week after the Scottish Secondary Teachers' Association handed in a petition to the Scottish Executive protesting about the outcome of job-sizing for promoted staff, which has led to lower salaries for over two-thirds of promoted posts in secondary schools.
The SSTA is widely seen as using the issue to build its membership at the expense of the Educational Institute of Scotland.
The larger union continues to abide by the teachers' agreement which led to the job-sizing exercise and to which the SSTA, it points out, was a party.
Ronnie Smith, the EIS general secretary, used his annual conference speech to condemn the breaking of ranks by the SSTA. No teacher was being devalued, he said in response to SSTA claims that promoted staff costs are being reduced in the secondary sector to pay for more management posts in primary. Mr Smith said it was the posts which had been job-sized, not individuals. The EIS received heavyweight support this week from Peter Peacock, the Education Minister, and from Dan Brown, the veteran negotiator who is head of personnel at the Convention of Scottish Local Authorities.
Mr Peacock said: "All sides signed up to job-sizing, not only in principle but in terms of how it would be achieved. I can understand that some teachers will feel unhappy at the outcome - that is an inevitable consequence of securing real and lasting change - but no one will lose out financially."
"This was part of the deal and it remains part of the deal."
But David Eaglesham, the SSTA's general secretary, said it continued to take issue with the approach used by PricewaterhouseCooper to carry out its study.
"The set of criteria used is arbitrary and brings about a vastly greater element of downgrading than was ever contemplated when teachers voted for the agreement," he said.
The SSTA believes its claim of arbitrariness is borne out by the vastly differing degrees of downsizing. The average of 68 per cent of posts downsized ranges from 51 per cent in West Lothian to 87 per cent in Shetland and Stirling.
For headteachers, 58 per cent on average have seen salaries for their posts reduced, ranging from none in Shetland to all in South Ayrshire and Stirling.
In the case of deputes, 87 per cent have been downsized across Scotland ranging from 50 per cent in Dundee to 100 per cent in Angus, Clackmannanshire, East Lothian, East Renfrewshire, Inverclyde, Moray, North Ayrshire, Orkney, Perth and Kinross, Shetland, South Ayrshire, Stirling and the Western Isles.
Principal teacher posts have been downgraded by 68 per cent on average, ranging from 50 per cent in West Lothian to 88 per cent in Shetland.
Mr Eaglesham claims authorities have been "reducing scores at will" even though the exercise led to some increases. "This gives the lie to any suggestion that the process was fair or transparent," he added.