Education secretary Michael Russell has ratcheted up the pressure on Scottish councils to improve short-term supply teachers' pay, which he says is the main barrier to reaching a pay deal for the profession as a whole.
However, local authorities have hit back, saying a resolution to the ongoing teachers' pay negotiations will take movement from all sides - councils, teaching unions and the Scottish government.
It would cost "several millions of pounds" to restore supply teachers' pay, halved to pre-2011 levels in the last teachers' agreement two years ago, according to councils. Under the current budget settlement from the Scottish government "councils simply cannot afford to absorb this cost", they say.
It is now looking increasingly unlikely that a pay rise for teachers will be agreed before the summer holidays.
A provisional deal over teachers' working conditions was reached in February by the tripartite negotiating committee, the SNCT. However, pay talks, which have been ongoing since January, have stalled over the issue of short-term supply teacher pay.
Scotland's largest teaching union, the EIS, wants supply teachers' pay, which was reduced for periods of five days or less in 2011, to be restored. But Cosla - which represents Scottish councils - claims the move would be unaffordable.
TESS understands that Cosla is also sceptical that pay cuts, rather than workforce planning, are behind Scotland's supply crisis, which has resulted in schools extending assemblies and students being left in canteens because cover was not available.
Now the education secretary has entered the fray, stating at the EIS conference on Saturday that the Scottish government and the EIS are "on the same side", implying that Cosla - the only other party at the table - is the barrier to a resolution.
Mr Russell made his comments during a question and answer session after he became the first education secretary to address the union's annual conference.
EIS president Susan Quinn revealed that a seven-week absence in her own school had resulted in just two days' cover. She asked if the education secretary was aware of the supply crisis and what he was going to do to tackle it.
Mr Russell admitted that there was a crisis and said action needs to be taken. The issue has to be "tackled and resolved" through the SNCT, he said, adding that the EIS and the Scottish government are "on the same side".
Billy Hendry, a spokesman for Cosla, described Mr Russell's comments as "disappointing and populist".
He continued: "Cosla has looked closely at the impact of changing supply rates back to the level which existed up to 2011 and the cost runs into several millions of pounds. Councils simply cannot afford to absorb this cost and so talks continue within the SNCT to try to find a way forward."
The SNCT meets again on 27 June, but insiders believe a deal is unlikely. However, the expectation is that any pay rise agreed for teachers in the future will be backdated.
- March 2011 - three-year teachers' agreement ends.
- May 2011 - new two-year deal struck. While the deal guarantees teacher numbers at 51,131 full-time equivalents, it also includes a two-year pay freeze and a cut to short-term supply teachers' pay, sparking an onslaught of criticism.
- November 2012 - Cosla offers a 1 per cent pay rise to all public sector workers but teaching unions refuse to fall into line.
- January 2013 - teachers' pay and conditions negotiations begin at the SNCT ahead of the pay freeze ending in March.
- Present - a provisional deal over teachers' working conditions has been struck but no deal reached over pay.