Pope Francis has said that he's firmly opposed to the teaching of gender theory to children in schools, arguing that the idea that "everyone can choose their own sex" is the "exact opposite" of God's creation.
"Today, children are taught this at school: That everyone can choose their own sex. And why do they teach this? Because the books come from those people and institutions who give money," Francis told Polish bishops last week, according to Catholic Herald.
"God created man and woman; God created the world like this and we are doing the exact opposite."
Francis added that Pope Emeritus Benedict XVI, his predecessor, agreed with the warning, and said that "we are living in an age of sin against God the Creator."
The Vatican leader added that "very influential countries" push this form of thinking, which he described as "ideological colonisation."
Francis said that gender theory is connected to the exploitation of humans and of the natural world, which he argued come from a failure to appreciate God-given dignity.
"It is a global problem: the exploitation of creation and the exploitation of people. We are living at a time when humankind as the image of God is being annihilated," the Catholic leader asserted.
Francis has spoken out against gender theory on a number of occasions, and in April 2015 said that it is wrong to ignore or diminish the differences between men and women in society.
"Getting rid of the difference is the problem, not the solution," Francis said in a speech back then.
"For example, I wonder if so-called gender theory may not also be an expression of frustration and resignation that aims to erase sexual differentiation because it no longer knows how to come to terms with it," he added.
The pontiff has rejected the notion that God calls for subordination, however. He said that both men and women bear the image and likeness of God.
"In God's plan, sexual differentiation is not ordered to subordination, but to communion and procreation. This reciprocity brings harmony and enrichment to the human family," Francis said at the time.
There has been controversy this past year in the United States over gender identity in public schools, with President Obama issuing a directive in May ordering public schools to allow boys in girls' bathrooms and locker rooms if they identify as female.
U.S. Attorney General Loretta Lynch claimed that Obama's decision was made in an attempt to counter bullying against transgender students.
"There is no room in our schools for discrimination of any kind, including discrimination against transgender students on the basis of their sex," Lynch said at the time.
Obama later said that his understanding of the Bible and his Christian belief guided his decision, pointing to the Golden Rule.
"What happened and what continues to happen is you have transgender kids in schools and they get bullied and they get ostracized and it's tough for them," the president said.
Some megachurch pastors in America, such as Robert Jeffress of First Baptist Church in Dallas, Texas, slammed Obama's directive, however.
"Gender identity confusion is an emotional disorder, that should be treated professionally, and compassionately. Gender identity confusion should not be exploited by social activists like those in the Obama administration who want to deny the God-given distinction between the sexes. This is a rebellion against God's plan," Jeffress said in May.