Lawmakers in Hungary have approved measures that effectively prohibit gay and lesbian couples from adopting children and define marriage as a heterosexual union.

According to Reuters, lawmakers amended the nation's constitution to define family as “based on marriage and the parent-child relationship. The mother is a woman, the father is a man.”

“Hungary defends the right of children to identify with their birth gender and ensures their upbringing based on our nation's constitutional identity and values based on our Christian culture,” the document states.

Gay couples were previously allowed to adopt if one partner applied on their own.

Under the new constitution, only married couples can adopt children, effectively prohibiting gay couples. Hungary recognizes gay couples with civil unions.

Amnesty Hungary criticized the move.

“This is a dark day for Hungary's LGBTQ community and a dark day for human rights,” said David Vig, the group's director.

Earlier this year, Hungarian lawmakers passed a law that prevents people who identify as transgender from changing their gender on official documents.

(Related: After attending gay sex party, anti-LGBT Hungarian lawmaker resigns.)