At their annual conference on the weekend, the NSW Young Nationals passed motions supporting same-sex marriage, and hit-out at those opposing marriage equality, expressing "disappointment and disillusionment" with the actions of their federal leaders.

NSW Nationals Women's Council chairwoman Claire Coulton, the daughter of Mr Coulton, questioned why the reform had been delayed by the federal party room.

"I believe, as most members of my generation do, that it's about equality for people who are our friends and our family members," she said.

"It's a shame when something that is publicly supported becomes a game of political cat and mouse, and I think that's been disappointing to a lot of coalition supporters."

Only three of the 21 member federal Nationals party room have publicly backed the reform. Mr Cobb and Mr Coulton are on record as opposing same-sex marriage.

By voting in favour of marriage equality at their annual conference in Corowa, the NSW Young Nationals have become the first youth division of a conservative political party to do so in Australia.

The youth wing of the junior coalition party have said it was an important issue in regional Australia and that "a young homosexual man living in regional NSW is six times more likely to commit suicide" than other members of the community.

The move was praised by Australian Marriage Equality's Rodney Croome for sending "a message to leaders of the coalition government that they are out of step with young voters, including young conservatives".