Pro-life protesters' signs labelled 'sick' by Justice Minister Andrew Little

A group of determined anti-abortion protesters marched at Parliament with graphic signs labelled "sick" by the Justice Minister.

They're protesting the progression of abortion legislation which will mean abortion is no longer a crime.

On Tuesday pro-life signs carried by protesters depicted graphic images of aborted foetuses - Newshub has decided to blur them.

It's been labelled a step too far for politicians.

Prime Minister Jacinda Ardern said the images were not okay.

Justice Minister Andrew Little went a step further, saying the images were "pretty sick".

The protest comes as the Abortion Reform Bill heads to Parliament for the second reading on Tuesday.

Under the new legislation a woman under 20 weeks pregnant would be able to refer herself to an abortion provider - she wouldn't have to undergo a medical test first.

After 20 weeks, a test will apply. That test has now been strengthened, meaning two doctors will have to agree an abortion is the right decision. 

It won't be necessary for many women. Just 0.5 percent of abortions take place after 20 weeks, usually due to extreme complications. It's a serious procedure that takes place in a hospital. 

Little says the changes will allow women to know they're making the best choice for themselves.

"It reflects what's happening anyway. I think women that have to make that decision when it gets to that point - they want to know they are getting the best possible advice," he told Newshub.

Progress of the abortion reforms have been fraught with painstaking negotiations to get to this point, especially between New Zealand First and Labour.

Another hurdle is in the works - NZ First wants it all to be decided by voters in a referendum, though that's unlikely to be voted through. 

"We want the people to speak not a group of temporarily empowered politicians," said Deputy Prime Minister Winston Peters.

Politicians will deliver a conscience vote on the referendum on Tuesday night.