Lessons on gay marriage and other same-sex relationships should be compulsory in schools, according to an amendment tabled by Labour.
The party is demanding changes to the Children and Families Bill, which would make lessons on same-sex relationships mandatory.
The amendment, due to be voted on next Tuesday, would also make issues such as consent, equality and abuse a compulsory part of the national curriculum.
Many are concerned about the damaging effects legalising gay marriage could have on civil liberties.
Leading human rights lawyer Aidan O’Neill QC wrote that parents would have no right to insist their children are withdrawn from school lessons across the curriculum that approve of same-sex marriage.
He also said teachers could be forced out of their jobs if they fail to endorse gay marriage in the classroom.
A poll for the Coalition for Marriage showed that more than 40,000 teachers say they will probably refuse to teach about “the importance of” same-sex marriage.
The ComRes survey found that one in ten teachers say they are likely to refuse to teach about gay marriage.
Another leading employment lawyer warned of the effect redefining marriage would have on teachers.
John Bowers QC explained that legislation currently “gives a privilege to marriage in the school curriculum”.
However if same-sex marriage was brought in to law, the current definition of marriage would change.
Mr Bowers said: “The stark position in my view is that a Christian teacher (or indeed any teacher with a conscientious objection) may have to teach about (and positively portray) a notion of marriage (and its importance for family life) which they may find deeply offensive.”
“If the Marriage Bill becomes law, schools could lawfully discipline a teacher who refused to teach materials endorsing same sex marriage.”