A group of teachers, parents and academics have launched a new organisation calling for a No vote in the marriage referendum.
The group says that the proposal has serious consequences that have not been properly dealt with in the public debate.
The group referred to evidence from other countries where, after the introduction of same sex marriage, teachers came under pressure to radically change their education practices.
A spokesperson for the group, Kevin Leavy said: "The reality is that if this referendum passes, gender-neutral 'marriage' would be elevated to a new status in the Constitution, and employees of the State would be obliged to protect that new model of marriage.
"As teachers, our fear is that for example, a teacher who gives preferential treatment to a view of marriage as between a man and woman over a same sex marriage, will be seen to be discriminating."
He said that the proposal will change the way that sex education classes in schools would have to be taught.
He also claimed that teachers who do not believe that same sex marriage is the same as marriage between a man and a woman could be accused of being “homophobic” and in breach of the Teaching Council Code of Conduct.
Mr Leavy said: "We already have material being sent into primary schools with the approval of the INTO called ‘Different Families, Same Love’.
"Among other things this advises teachers on how to teach children in Junior Infants about transsexuality and the different varieties of adult sexual desire before they even know the basic facts of life.
"If the referendum passes, it will become more and more difficult for teachers to refuse to teach material they believe is entirely age inappropriate."
He said that it must be taught in line with a school's ethos.
He said: "As educators, we fully support action against bullying, teaching tolerance and respect for all people. But we believe this must be done in a manner that is fully in harmony with personal conscience, school ethos and parents' values.
"If the referendum is passed, far-reaching changes involved in the redefinition of marriage will create challenges for educators which, in some cases, could lead to a loss of livelihood because of disciplinary action. It is highly unlikely that school ethos will provide sufficient protection, especially for teachers paid from the public purse."
"It is wholly unacceptable for the Government to accuse people of scaremongering for raising these entirely legitimate concerns. The Government has repeatedly refused to address any of these concerns and they are continuing to side step the issue at every turn.
"In fact, they have refused to consider including a conscience clause. The impact on the education system in other countries after the introduction of same sex marriage points to what would happen here.
"Teachers, and indeed parents, have not been informed or consulted about these consequences. Accordingly, we urge parents and teachers to vote No."