The Andrews government last week rejected calls to grant religious agencies special exemptions that would have given them the right to refuse placing a child in the care of a same-sex couple.

The Australian Christian Lobby had been pushing for the exemptions for months, arguing that some agencies could be forced to close unless they were protected under law to preference heterosexual couples, in line with their religious beliefs.

However, Equality Minister Martin Foley rejected this, saying the government had committed to removing discrimination in the Adoption Act "at any level" and that "genuinely equality, particularly for LGBTI people, should not be something that's up for some kind of debate."

Asked for his views on the matter, Mr Guy said while he supported giving gay couples the right to adopt, he would not be in favour of any move that undermined religious institutions.

"I'm broadly supportive of this issue, although it has to be said I won't be broadly supportive if it involves penalising churches," he said.

"Churches can choose who gets married in their church, or who takes communion in their congregation. A synagogue can choose, a temple can choose, a mosque can choose… I just can not see why the Labor government again wants to go to war with faith-based organisations."

The government will soon introduce new laws giving gay couples the ability to jointly adopt children, most of whom are already under their care through foster parenting or blended family relationships.

But while Coalition MPs are likely to get a conscience vote on the bill, Mr Guy's latest comments suggest the opposition could also try to amend the legislation to ensure religious exemptions apply. Such protections were granted in NSW when same-sex adoption was legalised there in 2010.

Labor only has 14 out of 40 seats in the upper house and would therefore require support from the Greens and the crossbench to vote down such an amendment, and would also need to wrangle seven votes to ensure its own adoption reforms pass.

Greens MP Sam Hibbins said his party would oppose any amendments from the Coalition to allow religious agencies to discriminate.

"Religious organisations providing services to the wider community should not be able to discriminate on the basis of sexuality or gender identity," he said.

Allowing gay adoption would bring Victoria into line with NSW, the ACT, Tasmania and Western Australia by giving gay couples and their children equal protection and certainty under the law, regardless of how their family was formed.