Senior Labor frontbencher Penny Wong has warned a plebiscite could put marriage equality “out of reach” in the same way a referendum sank the campaign for a republic.

“The [plebiscite] road is high risk and could put this out of reach in a way that the republic has been put out of reach,” Wong told Guardian Australia.



“I think that Turnbull has been prepared to countenance that is a real indictment.”



Her comments came amid uncertainty over whether parties who favour a parliamentary vote on same-sex marriage would vote down a Coalition bill to set up a plebiscite on the issue.

Both Labor and the Greens have reiterated their opposition to a plebiscite and have not ruled out blocking a bill.

Asked if Labor would support the plebiscite legislation, Wong said “if marriage equality is your focus, vote Labor because what we are saying to people is we will do what needs to be done – no one has seen the [plebiscite] bill.”

The Greens LGBTI spokesman, Robert Simms, told Guardian Australia he could not say whether his party would block the plebiscite because the bill to set it up had not been released and the party room had not debated it.



“We’ve been clear on this – we want to see a free vote in the parliament on marriage equality,” Simms said. “We’re very concerned about the impact a plebiscite would have. It would provide a forum for hate speech and it’s completely unnecessary,” he said.



Nick Xenophon, who could hold the balance of power in the Senate, is a supporter of marriage equality. He told Guardian Australia that while his preference is for a parliamentary vote on the issue, he would support a plebiscite “if that was the only option” to get the issue resolved.



He said any plebiscite should be binding, while noting it was “constitutionally difficult”.



“If there is a vote in parliament for marriage equality I will vote for it,” Xenophon said. “If that fails and the only option is a plebiscite then I will support that.”

Xenophon combined with other crossbench senators in October 2015 to call for a plebiscite to be held on election day.

On Monday, Malcolm Turnbull refused to comment on the “hypothetical” question of whether the Coalition would hold a parliamentary vote if the Senate blocked the bill to set up a plebiscite.

“If we are successful on 2 July, then I have every expectation that the parliament will swiftly legislate for a plebiscite and [it] will be held shortly after parliament resumes … so I would hope that the plebiscite could be held before the end of the year,” he said.

But the election debate has already provided a window into what may occur in the lead-up to a plebiscite.



At his campaign launch on Sunday, Bill Shorten described the plebiscite as “a taxpayer-funded platform for homophobia”. Lyle Shelton, the Australian Christian Lobby managing director, described his comments as “emotional blackmail”.

“There are legitimate ethical issues associated with deliberately denying children the love and nurture of their biological mother or father,” Shelton said.



Wong said there was no doubt the plebiscite, promised by Tony Abbott and backed by Turnbull, would lead to “hate speech” and could set back the cause of marriage equality indefinitely.



“The dismissal by the Liberal party and the National party of this being a licence for hate speech demonstrates a complete lack of empathy,” Wong said.

“It’s really disappointing to the LGBTI community that Mr Turnbull has become Tony Abbott on this issue because we live this issue.

“When Mr Turnbull says he wants a respectful debate, everyone knows he hasn’t even been able to get his own people to engage in a respectful debate.”



Wong is Labor’s leader in the Senate and the most senior member of the parliament who is openly gay. Labor is going to the election with six candidates who are openly gay, the Greens have 23 candidates and the LNP has five.

She said LGBTI candidates were important because “a parliament best serves a community that they more closely represent”.

Wong, who has two children with her partner Sophie, said the parliament and the community had come a long way since she entered parliament in 2002.

“My experience is prejudice does not survive personal interaction and personal engagement and personal connection except for people who are very committed to their own bigotry,” Wong said.

“Notwithstanding how upsetting it has been, some of this debate, some of the really hateful things that have been said including by Malcolm Turnbull’s own team, I think it has been heart warming in many ways, people’s response to our kids, when our daughters were born.”

The Coalition campaign spokesman, Mathias Cormann, characterised Labor’s opposition to a plebiscite as a lack of trust in the Australian people. The environment minister, Greg Hunt, described the referendum as the “ultimate democractic act”.

“Bill Shorten clearly doesn’t have much confidence in the Australian people,” said Cormann.

“That is our position and we have great confidence that people around Australia will conduct that debate appropriately.”

In May, the attorney general, George Brandis, told Senate estimates preparations for the plebiscite were “well advanced” and ruled out any suspension of anti-discrimination law for the campaign.



However, the government has not yet decided whether to give public funds to the yes and no camps.