The Andrews government is facing pressure to give faith-based adoption agencies the right to refuse to place a child in the care of gay couples, and for parents to be able to nominate that only straight families can adopt their child.

As the government prepares to legalise gay adoption in Victoria, the Australian Christian Lobby has warned that certain agencies could end up closing unless they retained the right to preference heterosexual families over same-sex families.

In a submission to the government's review of the Adoption Act, the group has pointed to similar amendments introduced in NSW to ask for a religious exemption that would give faith-based organisations the right to choose couples in accordance with their ethos.

The group has also called for parents whose children are being adopted to have the ability to choose a straight family on the grounds it is in the interest of the child to have a traditional "mother and father".

"The intent of faith-based agencies who preference opposite-sex couples for adoption is in good faith and in accordance with their religious principles and the best interests of children," the submission says.