The union that represents Ontario elementary public school teachers vowed to "vigorously defend" any educator who uses the modernized sex-ed curriculum in the classroom this school year in defiance of the province's decision to impose an older version.

The Elementary Teachers' Federation of Ontario (ETFO) denounced the Progressive Conservative government's plan to replace the current health and physical education curriculum — revised in 2015 — with a 20-year-old version. This includes sexual education.

President Sam Hammond called the move "reckless."

"Teachers will not be muzzled by a government whose political agenda takes precedence over the protection and education of their students," Hammond said in a speech opening the organization's annual meeting in Toronto on Monday.

"We need to prepare students for the world of 2015, not the world of 1998."

He added the province's plan is in direct conflict with teachers' responsibilities and obligations toward their students, stressing it's their duty to ensure children's safety and protect fundamental human rights.

ETFO represents 83,000 teachers across the province.

The ETFO will advise its members to 'continue to exercise their professional judgment' when it comes to teaching all sections of the current curriculum. (Shutterstock/Syda Productions)

Last week, six families launched a human rights challenge to the PC's repeal of the sex-ed curriculum.

Hammond echoed support for the lawsuit, explaining the outdated program jeopardizes the safety of students and violates the Ontario Human Rights Code and the Canadian Charter of Rights.

"They infringe upon the freedom of speech of teachers to provide proper education to their students," he said.

ETFO has instructed its legal counsel to intervene in any proceeding before the Ontario Human Rights Tribunal.

We need to prepare students for the world of 2015, not the world of 1998. - Sam Hammond, ETFO president

The PC's plan to scrap the revised program is a temporary measure while parents are consulted to craft a new document, Education Minister Lisa Thompson previously said.

Still, the 1998 curriculum lacks information about consent, gender identity and sexual orientation, education experts say.

Government officials have said some aspects of the modernized curriculum — rolled out by the Liberal government in 2015 — will be taught this September. But educators say it's unclear what aspects they will be allowed to teach and what punishment they would risk by teaching the latest curriculum.

Hammond explained more than 24 Ontario school boards have attacked the curriculum rollback since it was announced last month.

"We acknowledge the strong response of Ontario school boards concerning this issue and appeal to them to join us in this action by supporting teachers who demonstrate care and concern for their students," he said.

"Our students deserve as much."