On the eve of a three-day teachers' strike in Madrid, regional premier Esperanza Aguirre further enraged educators with another of her typically barbed comments.

"If education is obligatory and free in certain age groups, maybe it shouldn't be free and obligatory in subsequent age groups," Aguirre stated. Free-but-voluntary schooling in Spain is currently available for three-to-16-year-olds, students studying the Baccalaureate and vocational training.

The Madrid premier had previously attracted the ire of teachers in the region by accusing them of complaining about working "just" 20 hours per week — the amount of contact time teachers clock in a working week of 37.5 hours.

In Madrid, some 21,000 high school teachers are expected to heed the labor unions' call to arms to protest against longer hours and cuts in the number of supply teachers. The unions state that some 3,000 such educators are under threat from the proposal.

In Galicia, 30,000 public teachers are expected to down chalk today between 10am and 10.30am, with a further strike slated for September 27. Across the country, a "day of struggle" has been called against cuts in a further eight regions.

During protests last week in Madrid, Aguirre accused attendees of being "full-time unionists."