LEADERS of Sydney's major Christian churches will make a coordinated appeal against same-sex marriage straight from the pulpit this weekend in a bid to rally opposition before the federal parliamentary vote.

Statements from Anglican, Catholic and Greek Orthodox church leaders will be read out or distributed at services, stressing the need to head off any change to the current definition of marriage.

Archbishop Peter Jensen at St Andrews Cathedral. Credit:Lisa Wiltse

The move comes as proposed same-sex marriage legislation is due to be debated for the first time in the lower house on Monday, when a social policy and legal affairs committee inquiry report into two private members bills amending the Marriage Act will be tabled.

The Anglican Archbishop for the diocese of Sydney, Peter Jensen, writes to parishioners that the ''parliamentary success of this revolutionary redefinition is not inevitable,'' and calls on Christians who support the traditional definition of marriage to make their views known to federal MPs.