The Coalition for Marriage is without a venue for a same-sex marriage No campaign event in Tasmania, after the Wrest Point Casino cancelled its booking and UTAS refused to take it, campaigners claim.

Political Posting Mumma, aka Marijke Rancie, as seen in a video on her Facebook page. ( Facebook: Politicalpostingmumma )

The coalition was set to host a rally at the casino's 600-seat Plenary Hall on Friday, spruiking speakers such as senator Cory Bernardi, the Australian Christian Lobby's Lyle Shelton and "Political Posting Mumma" — who the coalition describes as a "Facebook sensation".

A contract was signed on Monday, and fees for the hire were paid on Tuesday. The group was informed on Wednesday the venue was "no longer available".

The coalition's Monica Doumit said she has been left scratching her head.

"We made some inquiries last week, and the Wrest Point casino came back and gave us options for two different rooms," she said.

"It doesn't make a lot of sense, it's possible two other events booked in over the last few days, but I don't know.

"All they would say is that the venue was not available, and offered a full refund."

Ms Doumit said she was not told the cancellation was due to the nature of the event.

"Businesses get caught in the cross-hairs of these events," she said.

She said a venue interstate had to cancel a No campaign event for security reasons after receiving threats, but most had run without incident.

"We've had other issues, like advertising companies decline to work with us, which is fine — we're all for free speech and we don't want people being asked to do things that are against their conscience."

A guest speaker billed for the event, Australian Conservatives leader Cory Bernardi, said questions needed to be asked of the casino.

"I think there are legitimate questions to be asked why a venue that has been booked and paid for has suddenly become unavailable with no reason given about why," Senator Bernardi told News Corp.

Senator Cory Bernardi blasted the casino's "terrible business practice". ( AAP: Sam Mooy )

"If nothing else it is a terrible business practice."

The $10 tickets are still on sale, but with a venue now "to be advised".

Ms Doumit said she was confident the coalition would find an alternative venue.

Head of the Catholic church in Tasmania Archbishop of Hobart Julian Porteous is also on the list of speakers along with Heidi McIvor who has featured in the No campaign's television advertisements.

University rejected us too, says Archbishop

After Wrest Point's rejection the No campaign sought to hold its function at the University of Tasmania, but were denied there too, according to a statement from Archbishop Porteous.

"Upon making enquiries to the University of Tasmania to secure a venue for the event, the university decided it [the event] did not meet its criteria.

"It is the essence of a democratic society that both sides of a debate have the right to present their case.

"To have the No campaign denied access to venues in order to express their views is a direct challenge to freedom of speech in our society."

The university has been contacted for comment.

Information for the event states "many parents are concerned about their rights as radical gay sex education classes become more widespread and even compulsory".

"Changing our marriage laws also gives licence to gay activists, weaponising anti-discrimination legislation and using it to stifle debate or dissent.

"Leaders in the gay marriage movement have already sought to use human rights and anti-discrimination commissions to target religious figures who have spoken out against same-sex marriage like Tasmanian's own Archbishop Porteous."

In a statement, a Wrest Point spokesperson said the casino "could not accommodate the booking in the required timeframe".

The event was to take place at Wrest Point's Plenary Hall. ( Supplied: Wrest Point )

Political Posting Mumma booked to speak

Promoted guest speaker at the Coalition For Marriage event, Political Posting Mumma — aka Marijke Rancie — says her Facebook page is "a safe space for anyone concerned about children being sexualised and politicised. We don't believe in gender theory and we don't support Safe Schools Curriculum".

Ms Rancie's Facebook page, which has about 9,400 followers, features posts attacking the Safe Schools Program and the Yes campaign.

In one video posted on her page in September, Ms Rancie states she is "not connected" with the Australian Christian Lobby.

News Corporation has reported Ms Rancie as being employed as a staffer by Victorian Liberal MP Michael Gidley.

The Hobart City Council, which has been a very public backer of same-sex marriage, said all community groups were free to use the council's venues.

When asked by the ABC whether the council would accept a booking from the coalition, the council's general manager Nick Heath said venues were available for hire.

"As such, applications from organisations and community groups are welcome," Mr Heath said.

The council made headlines when it installed a rainbow flag on the Town Hall, vowing to keep it there until same-sex marriage was legalised.