Equality advocates are warning an extra religious freedom bill headed for Parliament in the coming months could act as "payback" for Australia's same-sex marriage reform, by putting the traditional "man/woman" definition of marriage back into federal legislation.

In a sign of a new front opening in the religious freedom debate, LGBTIQ+ leaders are anxiously waiting to see a copy of a so-called "omnibus bill", which is separate to the religious discrimination bill Attorney-General Christian Porter is preparing to introduce to Parliament.

Equality advocates fear the religious discrimination debate will try and wind back the gains of the 2017 same-sex marriage reform. Credit:Lukas Coch/ AAP

The omnibus bill, which the Department of the Prime Minister and Cabinet lists for the winter/spring parliamentary session, is due to address some of the recommendations from Philip Ruddock's 2018 religious freedom review that will not be picked up in the main religious discrimination bill, or dealt with elsewhere.

These include a special provision for religious charities to continue to publicly advocate for a traditional view of man/woman marriage, and for this not to affect their charity status. It is also expected to include an amendment that makes it clear religious schools can refuse to provide facilities, goods and services to same-sex couples - who may want to use a school hall for their marriage ceremony. It is understood this might be an issue in country towns where there are limited community facilities.