A court Tuesday exonerated four leaders of the progressive Korean Teachers and Educational Workers' Union who were accused of leading anti-government campaigns last year.
Judge Kim Gyun-tae of the Jeonju District Court in North Jeolla Province said the campaigns expressed the political views of the individuals and that they didn't interfere with their jobs as teachers.
Kim said a law should not restrict the constitutional right of a person to speak freely. The announcements did not harm anybody, he added.
The prosecutors vowed to appeal.
The prosecution indicted a total of 89 members of the union last year, saying that they broke the Civil Servant Law prohibiting them from engaging in political activities and taking collective action.
There are 15 more trials of teachers facing similar charges, and Tuesday's verdict is expected to have an effect on them.