Marriage Alliance is opposed to same-sex marriage. Its 30-second commercial declares: "It's time to step back and consider all the issues around same-sex marriage – like how it will affect children, or sex education in schools, or even what rights you could lose." Same-sex marriage is represented as a colossal iceberg and – in an apparent reference to the doomed Titanic – there is a ship about to crash into it. Viewers are then directed to the group's website. When asked if Channels Seven and Ten have the same rights as the Irish bakery to refuse certain jobs, York said: "The difference is ... it wasn't just a cake, it was a cake that bore an activist slogan supporting gay marriage.

"It had the children's character's Ernie and Bert on top of it, it would have gone out in the box of Ashers Bakery ... even though they're happy to serve all comers and provide cakes to all people who want them, they felt they shouldn't be coerced or cornered into creating something which was an activist cake for an event, and not have a choice about the matter. So they exercised their freedom not to be involved in it." Do Seven and Ten have the freedom not to be involved in what they might see as the activism of Marriage Alliance? "I think the difference is this," York said. "All we're doing is saying that we are offering a forum for people to debate an issue. And that forum is open to people even who support changing the definition [of marriage]. It's open to all comers. "We definitely have a position of supporting the current definition [of marriage]. But the difference is we are not going to turn away anyone who wants education about the issues ... what we're offering is information, a safe haven for people to learn about it."

York – who sought Liberal Party preselection in Bradfield in 2009 – lectures in law and has worked for the Royal Australian Navy. She said she views Seven and Ten's rejection of the ad partly as a "compliment" "They obviously looked at it and thought, 'It's devastatingly effective. Beautiful graphics, it's going to get everyone's attention, and it's a very powerful message.' That's my first reaction." But she said she is "disappointed and surprised", and also views it as a free speech issue. "It has demonstrated exactly the point that we are making. That, if we are to have a climate where we change the definition of marriage, all the indicators are that we will lose Australian human rights and freedoms.

"If it's already affecting us – if it's already affecting the environment, the cohesion of our society, and this is while there's a proposal on the table - how much worse will it be if the change is actually enacted into law? "It could only get worse." Some sources have suggested the ad was rejected because of Marriage Alliance's request for a tricky combination of 30-second and 15-second spots. But York isn't buying it – not least because Nine, Foxtel and Fairfax Media, publisher of this website, are currently screening the commercial. "I heard different things on the grapevine but [Seven and Ten haven't given a reason] that makes sense.

"The fact they couldn't fit it in just didn't make sense ... and it was a last-minute withdrawal. It's actually inexplicable." A Seven spokesman said: "We couldn't accommodate their booking request. That's about it." A Ten spokesman said: "As company policy, we do not talk about our commercial arrangements, out of respect for our advertisers." A Nine spokeswoman confirmed the ad is airing on the network "but in very selective timeslots". An SBS spokeswoman said no one had approached the broadcaster about the ad.

And a Foxtel spokesman, who confirmed the pay TV operator is showing the commercial, said: "As a company Foxtel is a strong supporter of marriage equality. We have given our support to Australian Marriage Equality by joining as one of the campaign's corporate supporters. "As a media company we also believe in free speech, therefore we do not believe it is appropriate to refuse any side the opportunity to put forward its views. Naturally, we will be running ads in support of marriage equality when they are launched shortly." Marriage Alliance has also posted its commercial on YouTube. However, comments have been disabled.