A teacher at a Kowloon Tong secondary school did not have her contract renewed by management after she allowed students to play Glory to Hong Kong - the "anthem" of local protesters - in a music exam.

This came as education secretary Kevin Yeung Yun-hung gave a big "no" to the singing of the protest song in schools.

In an e-mail to parents yesterday, Heung To Middle School described itself as a "patriotic school by tradition" guiding students to "love the country and identify themselves as Chinese."

The school said one factor that is considered when deciding whether not to renew a teacher's contact is whether he or she can implement the school's principles.

Music teacher Novem Lee Kwan-pui said on Monday that her contract would not be renewed, but the school failed to give her a reasonable explanation.

"In January, the principal told me the school board was not happy with my political stance, which is different from the school's," Lee wrote in an e-mail to colleagues and students.

"I was told the management thought I had discussed my own political views in a very 'high-profile' manner," she said, denying the accusation.

"This is because they heard that during a music exam, I did not ban students from playing what they considered an 'inappropriate song,' namely Glory to Hong Kong."

Yeung said the song "is obviously a political propaganda song" when asked if singing it would be banned in schools. nBut he said it is up to schools to decide what songs to prohibit, a day after he warned students against singing "any songs with political messages."

When asked whether songs from the Les Miserables, from which the protest anthem was adapted, could be used in singing competitions at school, he said: "I think it's fine, though of course you need to consider the environment and the purpose."

But singing the song Love Basic Law is not "political," just "a way to promote the rule of law," according to Yeung.

He also said students should focus on studies instead of advocating discussion of the proposed national security law, as authorities will develop teaching materials after the law is introduced. He then condemned school staff joining strikes, saying: "Is it professional to leave out students due to political reasons?"

Opposition activists are planning a referendum Sunday over whether to start strikes and class boycotts to protest the law.

Isaac Cheng Ka-long, spokesman of Hong Kong Secondary Students Action Platform, said that attacks from the government are "unprecedentedly stern."

"Students will not join the referendum during the time of classes, and there is no legal risk in doing so," he said, adding that authorities are trying to intimidate students.

Separately, the education bureau announced yesterday revised plans for public school teachers to undergo training sessions, including some concerning "professional values and conduct."

Teacher pays for allowing protest anthem in exam