Sinn Féin's Michelle O'Neill has accused other parties of "copping out" by allowing members freedom of conscience on the issue of abortion.
More than 20 Sinn Féin branches have tabled a motion for this weekend's ard fheis (conference) on the issue.
It argues all members should be allowed to speak and vote about abortion according to their consciences.
The Ulster Unionists, the SDLP and Alliance all adopt freedom of conscience approaches towards abortion.
However, interviewed for BBC Radio Ulster's Inside Politics, Mrs O'Neill, the Sinn Féin vice president, said legislators must implement policy for all people regardless of their own personal viewpoint.
Unlike other parts of the UK, the 1967 Abortion Act does not extend to Northern Ireland.
Currently, a termination is only permitted in Northern Ireland if a woman's life is at risk or if there is a risk of permanent and serious damage to her mental or physical health.
Ms O'Neill told the programme: "I think the other parties have actually copped out on this issue, that's my personal view and that's the view of the ard comhairle (Sinn Féin's ruling executive).
"We provide legislation for all people, your own personal opinion doesn't come into it.
"And that's why there's a differentiation between the membership and the view that you have and those people that legislate."
Mrs O'Neill added that "of course we are all pro-life, but this is legislating for women who find themselves in crisis, who find themselves in very difficult circumstances when they find themselves, for instance, with a diagnosis of fatal foetal abnormality.
"It's compassionate legislation, it's making sure we provide support to women here on the island of Ireland, because the reality is so many women are travelling to England to get support every year away from their family.
"It's about supporting women, because they have been failed for far too long."
Mrs O'Neill said that without pre-empting this weekend's debate, she felt confident that the Sinn Féin leadership's approach to abortion would get the support of the majority of delegates.
Sinn Féin has previously advocated abortion in cases of fatal foetal abnormality, rape and incest.
But problems have been pointed out, for example, in proving a rape allegation within the timescale necessary to perform a termination.
In the light of the debate about repealing the eighth amendment of the Irish constitution, the government in Dublin is expected to move towards a wider approach of legalising terminations within the first 12 weeks of a pregnancy.
A motion backed by Sinn Féin's leadership does not specify the 12-week period, but refers to making abortions available through a GP-led service "without specific indication for a limited gestational period".
Mrs O'Neill denied that this gives the Sinn Féin leadership a blank cheque to eventually back abortion in line with the 24-week period provided by the UK's 1967 Abortion Act.
Instead, she argued it allowed the party flexibility in case legislation brought before the Dail (Irish parliament) eventually reduces the time limit to 10 weeks.
Mrs O'Neill said that her personal view is that "12 weeks is the maximum, that's what all medical advice points towards".
The Sinn Féin vice president said she did not "want to lose one single person" over the issue of abortion.
Mrs O'Neill said she was confident Sinn Féin members are "mature enough to have an articulate debate" and then go out and back whatever policy is adopted.
- Inside Politics is on Radio Ulster on Friday at 18:05 BST.