One Nation’s Barnaby Joyce has joined pro-life campaigners to pile pressure on Nationals MPs to vote to criminalise some abortions ahead of a tight vote in New South Wales.

Anti-abortion activists have threatened to campaign for One Nation against major parties to force new limits on terminating pregnancies on the back of its polling surge.

Introduced to chants of “Nats must act,” Joyce addressed a rally against “sex-selective” abortions outside NSW parliament on Tuesday night.

“You must keep that fire burning for those people who can’t stand up for themselves, and I call them people, they’re not foetuses,” Joyce said. “They are people.”

“Politically, does this make you popular? Nup, nup. Probably lose half the votes every time you do it. But you know why you do it? Because it’s the right thing to do.”

He encouraged the crowd to campaign against sitting politiciansn on abortion.

‘The one thing politicians fear is losing their job,” Joyce said. “They’re very mindful of that. What I see before me here is about 1,500 people who can hand out how to vote cards.”

Dr Joanna Howe, who organised the rally and invited Joyce, told the crowd the four Nationals members of the NSW upper house were the only people standing in the way of the bill passingalthough it would still need lower house approval to become law.

“We are so close to passing the first-ever pro-life bill through a house of parliament this country has ever seen,” Howe said.

“The message to the Nats is: if the Nats don’t pass this bill, then One Nation is going to take your seats … If you don’t vote for this bill, Barnaby’s coming for you.”

The bill, moved by the Libertarian upper house member, John Ruddick, is a ban only on sex-selective abortion. Howe told the crowd that bill would be just the start of the legislative campaign.

“Business has changed,” she said. “Every year in this state, we will introduce a bill until we protect all the babies.”

She told Guardian Australia she next planned to lobby for a ban on late-term abortions.

Howe said Tuesday’s Sydney rally was her biggest pro-life rally yet and she planned to organise grassroots campaigns in every Nationals-held seat ahead of NSW’s state election in March 2027.

“Because there will now be One Nation candidates in those seats, we know that we can unseat pro-abortion Labor people, pro-abortion Liberal people and pro-abortion Nationals,” she said.

Speakers addressed Tuesday’s crowd from a truck with handpainted banners of two foetuses captioned “Emma and Ruth”, the names Howe attached to an image of what she thought were foetuses but were actually baby sugar gliders.

A counter-protest of about 150 people assembled nearby in Martin Place, where a University of Sydney student, Lucy, originally from the US, warned eight states had introduced sex-selective abortion bans like that being considered in NSW before Roe v Wade was overturned in 2022.

“They were able to get way with it in America and then they kept going bill by bill, chipping away at abortion rights, chipping away at freedom, until one day, we woke up and our bodies were apparently no longer ours to control,” Lucy said.

The NSW bill is the latest in a series of attempts to wind back abortion access since it was decriminalised in all states and territories almost three years ago.

The bill will be debated in NSW’s upper house on Wednesday and go to a vote in coming days, and, if passed, go to the lower house. No party has a majority in either house and Labor, Liberal and National MPs have been granted conscience votes on the issue.

Alex Greenwich, the independent lower house MP, said the vote would be tight, made worse by the suspension of a Labor minister, Penny Sharpe.

“Mark Latham and [Liberal] Damien Tudehope now control the upper house,” Greenwich said. “As such anything can happen.”