A children's birthday party organiser has stood by her decision to sack an entertainer who aired her opposition to same-sex marriage online, despite the decision drawing scorn from the No campaign.

Canberra business owner Madlin Sims said the woman, who dressed up as children's characters for Ms Sims' party business, had installed a frame on her private Facebook profile picture that said "it's OK to vote no".

Ms Sims said when her brother raised his disagreement with the post, the woman said she believed same-sex marriage was wrong and claimed she was being attacked for her religious beliefs.

In response Ms Sims took to Facebook, arguing advocating against same-sex marriage was homophobic "hate speech," adding she did not want her business associated with the contractor's views.

"This entertainer of ours, she had posted representing the business on the same platform — the Facebook page where this frame was shared," she said.

"Not in any way am I saying 'don't voice your opinion', that's democracy ... but I do feel that it is hateful being against gay marriage.

"Just like I wouldn't want someone who is racist working with us ... I wasn't comfortable having someone who was so out and proud about being against equality."

The woman was an independent contractor, and not a direct employee of Ms Sims' business.

In a Facebook post, Ms Sims said she could not have someone publicly representing her business "posting hate speech" because:

"1. It's bad for business

"2. I don't like shit morals

"3. I don't want homophobes working for me, especially in an environment with children."

Ms Sims expressed particular concern that the woman could be assigned to work with same-sex parents.

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"I was worried that if she were to be put in a situation like that that she might say something," she said.

Free speech has consequences: Sims

David Goodwin from the Coalition for Marriage, a leading voice in the No campaign, said the decision was deeply concerning.

Key dates in SSM postal survey: August 24 — the final day to register with the AEC if you want to take part in the survey

September 12 — survey forms start being sent out

September 25 — all forms are expected to have been sent

October 27 — forms are strongly encouraged to be returned by this date

November 7 — the final deadline to return surveys

November 15 — results are released

"The fact that you could share your own personal view on a matter like this and find yourself out of a job is extraordinary," he said.

"What this woman actually currently supports is the law of the land — is [Ms Sims] suggesting that she's not going to employ nearly half the nation?

"If that's acceptable now, I shudder to think what will become the norm after a vote goes through and the Yes campaign actually wins.

"We are going into terribly uncharted waters."

But Ms Sims said she felt compelled to "take a stand" against inequality, and did not like that her case had been portrayed as a free speech issue.

"It sucks that it's being portrayed as that because ... my brother tried to open up that conversation with her and she was pretty adamant," she said.

"Free speech is there and so is consequence.

"Just like I have to cop the backlash of what I've posted, this contractor, their consequence is losing their temporary work with us."