Former deputy PM Barnaby Joyce has recorded robocalls slamming a bill to decriminalise abortion in New South Wales.

Mr Joyce argues against decriminalising abortion in pre-recorded messages to NSW constituents, claiming that the bill will allow selective abortion based on the sex of the baby.

The Reproductive Health Care Reform Bill 2019 will allow terminations up to 22 weeks, as well as later abortions if two doctors, considering all the circumstances, agree the termination should take place.

Mr Joyce says that the bill allows legalised abortion for any reason "right up to the day of birth".

In the recordings, Mr Joyce says that he is calling on behalf of anti-abortion group Foundation of Human Development, a charity registered with Right to Life NSW.

The Member for New England has long been a critic of the decriminalisation of abortion in NSW. And, during question time in federal parliament at the beginning of this month, he accused the bill of declassifying fetuses as humans.

The bill passed the NSW lower house 59 to 31 in a conscience vote at the beginning of the month, which will remove abortion from the state's criminal code. It will be debated in the upper house on Tuesday.

Premier Gladys Berejiklian voted in favour of decriminalising abortion, along with her colleague Health Minister Brad Hazzard.

Premier Gladys Berejiklian has delayed the final vote in the upper house, which was set to be debated in parliament today, amid pressure within her party.

The chair of an inquiry into a NSW bill decriminalising abortion has dismissed concerns about the time given for examining the proposed laws, saying the issue has been debated since the 1960s.

Chair Shayne Mallard said the committee completed the work necessary.

"My personal view is that if we had six months we'd still have the same information. I can't see how anything would have changed," he told AAP on Monday.

Barnaby Joyce has been contacted for comment.

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