The Educational Institute of Scotland (EIS) said only a united front from educational professionals in schools and colleges could stave off threats to pensions and education services.
Larry Flanagan, the union's general secretary, said: "The strength of Scotland's teaching profession is in the unity of its teachers and lecturers, primarily through the EIS, which allows a vigorous defence of Scottish education.
"In the current climate of economic crisis, budget cuts and attacks on the employment, pay and conditions of public-sector workers, it is more important than ever that the teaching profession is united to protect Scottish education.
"You don't have to look very far to see the dangers posed if we do not stand together as teachers and lecturers – attacks on teacher pay and conditions such as the prospect of regional pay, the erosion of the comprehensive ideal and the damaging free-schools agenda, the continuing market-driven approach to education and the use of divisive and misleading league tables – all of these things are happening not so very far away from us here in Scotland.
"While we have managed to hold off these threats in Scotland, through a combination of teacher and lecturer unity and differing political priorities in Holyrood compared to Westminster, we must remain united to head off the current threats to our education system."
"I would urge all teachers and lecturers to make a unified stand in defence of our schools, colleges and universities and the rights of all who work and learn in them."