Thousands of anti-abortion protesters have rallied outside the NSW parliament after opponents of a bill to decriminalise abortion in New South Wales successfully delayed a final vote on the legislation until next month.

The parliament’s upper house began debating the reproductive healthcare reform bill on Tuesday, almost two weeks after it passed its first hurdle in the lower chamber.

Introducing the bill into the upper house, Labor’s Penny Sharpe said the legislation would change the law “to trust and respect women in this state”.

“Criminalising abortion does not stop abortion, it just makes it unsafe,” she said.

“We have heard the stories of our friends, our mother, our grandmothers, our aunties and our children. We have heard stories of the past where women were harmed or died seeking illegal backyard abortions and we are determined to never go back to those days again.”

A vote on the bill had been expected to take place this week but Guardian Australia has confirmed that will now not take place until the middle of September.

On Tuesday evening, thousands of anti-abortion protesters gathered in Martin Place and earlier in the day, a massive “choose life” was scrawled by skywriters above Sydney.

Holding up crosses, pictures of Jesus and signs saying “stand for life”, the protesters listened to speeches from MPs and religious leaders who oppose the bill.

It comes after a concerted campaign from opponents of abortion reform to derail the bill. On Tuesday the Liberal party MP Tanya Davies – who led the unsuccessful charge against the bill in the lower house – said the bill had caused a “crisis of government”.

Guardian Australia understands the premier, Gladys Berejiklian, urged the bill’s supporters to delay the final vote on the bill until the next sitting week which they have agreed to.

The bill will still be debated this week but amendments won’t be considered until the next sitting week beginning 17 September. A final vote will take place then.

The bill’s supporters remain confident it will pass the lower house, despite a backlash from rightwing MPs, religious leaders and conservative figures in the media who have mounted a concerted campaign to derail the legislation ahead of the upper house vote.

Conservatives outside the parliament have also railed against the bill. The federal Nationals MP, Barnaby Joyce, has recorded a robocall urging them to oppose the bill, claiming it would allow abortions to be performed “for any reason right up until the day of birth”.

Opponents have also seized on the so-called “sex selection” issue ahead of the vote next week, despite expert medical, legal and women’s groups saying there is no evidence the practice is an issue in NSW.

The bill has caused huge divisions within the Liberal party, pitting moderates including Berejiklian, the health minister Brad Hazzard and transport minister Andrew Constance against police minister David Elliott and corrections minister Anthony Roberts.

On Tuesday the conservative upper house Liberal party MP Matthew Mason-Cox said the bill would “undermine” the government’s agenda because of opposition from conservative crossbench parties.

“I’m very concerned – and I’ve raised it with the premier directly – that we are undermining our ability as a government to prosecute our agenda with what we’ve done with this bill,” Mason-Cox said.