EACH of the 21 Bendigo small businesses who publicly supported same sex marriage received an identical letter on Wednesday from a nameless person criticising the move.

The letter was the only direct negative response to the businesses, in addition to a handwritten note to one cafe and several comments on Facebook pages.

Robe Bendigo owner Fiona Rooke said positive feedback had far outweighed the negative.

"I'm not saying they're wrong," she said.

"The whole argument stems back to basic equality."

The letter listed seven reasons why it opposed the push for same sex marriage, including the "breakdown of the family unit", denying a child the roles of the mother and father and "opening the door for the promotion and encouragement of sexual experimentation within our schools".

Ms Rooke responded to the letter on their Facebook page, making special mention that the author of the letter wished to remain anonymous.

"I also support age equality, gender equality, disability equality, race equality and religious equality - pretty much any sort of equality that allows you the freedom to celebrate who you are and make the choices you choose," she said.

Cafe Cortille owner Jayson Tayeh said feedback was expected, as all were entitled to their opinion on the issue.

"We all received at least one letter and Facebook comments with a differing opinion, which is perfectly fine," he said.

"The fantastic thing has been the large majority that has given positive feedback. People have come in and said 'thank you' for what we did."

A second advertising campaign is in the pipeline from Bendigo businesses who support same sex marriage in Australia.

The organiser of the first campaign is seeking support for a second, larger effort after receiving support from more businesses.

The campaign featured a full page advertisement in last Saturday's Bendigo Advertiser.

Organiser Jayson Tayeh said the second advertisement would take a different approach.

"The original idea was to see who in 'my world' supports marriage equality," he said.

"Now we want to show who in 'our world' here in Bendigo supports it by using that six degrees of separation idea.

"Big or small, anyone who wants to get involved can email regionalmarriageequality@gmail.com."

Businesses have also been placing fliers in their front windows demonstrating their support for same sex marriage.

Kane Barri, of The Meadow, printed off dozens of the fliers in response to a letter all of the businesses received opposing their move.

He said they wanted to show that they were proud to hold their position in favour of same sex marriage, and in the face of "hat

"I expected people to be against it, but it was interesting to see someone actually write and mail 21 letters," Mr Barri said.

"The response we've had through has been great, we received something like 800 likes on Facebook and more than 100 comments of support."

The fliers in businesses' windows state "This business supports marriage equality" and is available for all.

Mr Barri also placed the original letter in his window from the person who opposed the businesses' stance, in which he describes the person as "gutless" and states "we definitely don't want your business anyway".

The businesses plan on placing another advertisement - potentially over two pages - in the June 20 edition of the Bendigo Advertiser.