The SA Democratic Teachers' Union (Sadtu) was destroying education in parts of the country, Western Cape Premier Helen Zille said on Friday.
Speaking during a debate on Youth Day in the National Council of Provinces, she called on government to enforce the sound policies it proposed, rather than "cower" before Sadtu.
Youth Day, on 16 June, commemorates the start of the 1976 Soweto uprising.
Zille said education defined a person's chances in life.
"I agree with President Jacob Zuma that every teacher should be in class teaching, and every learner should be in a class learning for seven hours every day."
For this reason, it was important that government strictly enforced such policies, "rather than cower weak-kneed before a specific teachers' union, which I call the Strike and Don't Teach Union".
She said Sadtu put the comfort of its members above those of children, and preferred mediocrity to excellence.
The union also held some provinces to ransom.
"The education that children so desperately need is systematically being destroyed in so many ANC-run provinces, most particularly Limpopo and the Eastern Cape. They are being held to ransom by the SA Democratic Teachers' Union."
Zille, who appeared drawn and tired, repeated her call for a youth wage subsidy, saying it was designed to offer opportunities to young people.
It "enabled young people to prove themselves" in a first job.
She warned that youth activism, "symbolised by the Class of 1976", was rising again.
"Youth unemployment is indeed a ticking time bomb, and it is tragic that the government... bluntly refuses to implement any key solutions to defuse this time bomb," she said.