"The wages of Swiss teachers are still significantly lower than those of professionals in other sectors with comparable entry requirements," said German-speaking Switzerland's teachers' union (LCH), which has called for a salary scale with regular increases to be enshrined in Swiss law.
The union argued that the lack of wage guarantees could deter the brightest workers from the profession, and said kindergartens and primary schools - where pay is particularly low - were already suffering from staff shortages.
LCH has regularly called for an overhaul of teachers' salaries since 2013, when it set a deadline of 2018 to give cantons and employers time to finetune the changes.
But on Monday, its managers said that one year before the deadline, "the salary situation is inadequate".
According to a union survey, teachers in three quarters of its member organizations rated the salary situation as bad or unsatisfactory.
And a study of wage change since 2013 showed that not only did many cantons fail to offer regular salary reviews or guaranteed raises, but many had seen increases in workload as well.
In the northern canton of Aargau, for example, there is no guarantee of an annual pay raise, while at the same time the number of obligatory lessons has increased - amounting to a "hidden wage cut". The same applied to Lucerne, where the increased workload amounted to a drop of around 3.5 percent in wages.
The union warned that cantons which fail to guarantee pay rises for increased workload risked losing their top staff to better-paying cantons.
What's more, the Swiss teaching profession as a whole could suffer, with graduates and experienced teachers looking elsewhere for guaranteed wages. A 2016 survey revealed that schools were in some cases already forced to hire "unqualified" staff.
In real terms, teachers' salaries have increased by 10.8 percent over the past 25 years, LCH said, citing figures from the Federal Statistics Office. This compared to an average increase of 14.4 percent across all industries, which rose to 30 percent in some sectors including chemistry, pharmaceuticals and financial services.
LCH set out its demands for 2018, calling for salaries which reflected both the profession's entry requirements and workload, as well as guaranteed annual raises and preservation of purchasing power.
These changes, the union said, would make teaching a more attractive profession, ensuring "appropriate and well-trained staff" continue to apply for jobs in Switzerland's schools.