THE brother of the Nationals' Bendigo-based senator Bridget McKenzie has publicly questioned her stance on same sex marriage.

In a 370-word letter, Alastair McKenzie, of Melbourne, described growing up gay in the country in the 1990s as "horrific" and labelled his sisters comments as "extremely hurtful".

Earlier this week, Ms McKenzie said she would oppose a bill seeking to legislate same sex marriage because "marriage is a sacred commitment between a man and a woman and should remain as such".

Mr McKenzie - a Nationals Party member - said public statements like those from his sister increased the feeling of isolation for young people in the country questioning their sexuality.

"Given her own story and connection, I had hoped to see a more courageous and compassionate response," Mr McKenzie said.

The letter detailed his re-connection with the country, returning to his mother's hometown of 400 five hours from Melbourne.

Mr McKenzie also outlines his reasons for supporting same sex marriage and labels some within politics as "homophobic".

Ms McKenzie chose not to comment on her brother's position, preferring to keep her family life separate from her political life.

"Since entering the Senate in 2011 I have worked hard to ensure my family life remains separate from my political life and therefore will not be commenting publicly on this matter," Ms McKenzie said in a statement.

Mr McKenzie's letter stated those living in the country were often unfairly labelled as "rednecks" in the city for their views and he held no grudges against country people.

"Most are intelligent and compassionate - many are connected to this issue personally, some being gay themselves, many indirectly through family members, work colleagues and friends."

He said marriage was more than just a word, describing it as a "social announcement" that all were entitled to.

"A secular society that chooses to legislate marriage should not discriminate based solely on the gender of consenting participants - that is by definition discrimination," Mr McKenzie said.

"We would think it absurd if we applied the same logic and explicitly denied marriage to citizens holding other attributes, such as the religious, people of a particular ethnicity or the disabled.

"Such flawed logic has no place in statute or civil society."

Read the full letter from Alastair McKenzie in Saturday's Bendigo Advertiser.