Teachers and alumni of Assumption College are giving its director until Saturday to step down and restore the reputation of one of the oldest and most prestigious Catholic schools in the country.
In a message posted on Facebook late Friday, they said they were waiting for an answer from Anan Preechawutthi and the St Gabriel's Foundation, which operates the school.
They accuse Mr Anan of mismanagement and lack of transparency in running the school and handling a promised salary increase for teachers.
Teachers, students and alumni join a rally against the director at Assumption College on Friday. (Photo by Thanarak Khoonton)
About 300 teachers, students and alumni calling themselves "Fight for Assumption", most of them in black, rallied at the school earlier in the day in what they called a mission to bring back glory to the school.
The school was thrown into confusion on Friday after the director abruptly closed it until Feb 1.
He said in a statement posted on the school's website that the closure necessary after "a group of ill-intentioned people" who gathered at the school were making it unsafe for students.
Confusion mounted later in the day when teachers opposing the director posted a message on Facebook, saying all classes would resume on Monday and extra classes for primary pupils would open on Saturday.
The conflict erupted after the school announced a plan to merge the primary section with the secondary campus, both in Bang Rak district. Some protesters suspect a business motive behind the merger, while teachers are worried that it could lead to layoffs.
But Sirichai Fonseka, a provincial superior of the St Gabriel's Foundation, said earlier that all teachers' jobs were safe. The merger had been planned for almost 20 years, he added.
Assumption College was established in 1885.