Former Prime Minister Sir Bill English has returned to Parliament to protest proposed changes to abortion laws, saying the way they treat health workers who object are "disgraceful".

But life-long abortion rights campaigner Dame Margaret Sparrow says the reforms need to go further.

A parliamentary select committee is currently hearing public submissions on legislation that would give women access to abortions until 20 weeks' pregnancy without having to go through current legal hoops, largely remove abortion from the Crimes Act and allow for the creation of "safe zones" around clinics to keep protesters away.

The legislation passed its first reading 94 votes to 23 in August and politicians now need to consider what changes could be made before it returns for a second vote.

Sir Bill and his wife, Doctor Mary English, spoke to the committee on Wednesday, the former, in graphic detail, describing the process of some late-term abortions and calling it "extreme violence".

The pair also raised concerns the wording of the law would open health workers with conscientious objections to abortions to be pushed out of their jobs.

The bill as it stands says employers – who would largely be District Health Boards – need to accommodate for objections "as long as it would not unreasonably disrupt the employer's ability to provide abortion services".

"This is the Government giving itself permission to harass its own vulnerable workers," Sir Bill said.

"It's a disgraceful piece of legislation."

Mary English said it could drive much-needed staff out of the sector and would particularly affect those from religious communities.

Dame Margaret Sparrow has been advocating for abortion reform since the 1970s. Photo / Boris Jancic

The argument was met with opposition from committee member and Green MP Jan Logie, who at one point entered a heated exchange with Sir Bill.

"It's hard to see for me how a large DHB or institution would be in a situation where a person could not be found to do other duties," she said.

The couple last year made a similar submission against assisted dying legislation currently being considered by Parliament.

Meanwhile, Dame Margaret Sparrow, who was the president of the Abortion Law Reform Association of New Zealand for more than 30 years from the 1970s and one of the first doctors in New Zealand to prescribe the morning-after pill, said the changes needed to go further.

She and other advocates for change have welcomed the legislation as a major step forward, but they've criticised the requirement for health practioners to still approve abortions after 20 weeks.

Dame Margaret was also critical of what she said was "scaremongering" about late-term abortions.

"Nobody is comfortable with a late-term abortion of a pregnancy … but I think creating horror stories is disrespectful to those very few women who sadly, often for complicated medical reasons, have to have a termination," she said.

"It's a matter of compassion, not violence."

She said if anything, there needed to be fewer provisions for contentious objection.

"The balance has to be in favour of the patient," she said.

"We have the doctors with their principles and their moral objections, but we also have the patient needing care, which is time sensitive."

Advocates for change have argued that abortion is the only medical procedure still in the Crimes Act and that the current state of the law means women have to effectively use a loophole in the law to get access.

There were more than 13,000 abortions carried out in 2017, almost all on the grounds it would be a danger to the woman's mental health.

Dame Margaret said it was time for a "more honest" system.

The Select Committee received more than 25,000 written submissions and is publicly hearing from 150 groups and individuals.

It is expected to report back in February, 2020.