Pro-lifers are decrying an amendment to the Public Order Bill that paves the way for the introduction of so-called 'buffer zones' around abortion clinics nationwide.
MPs voted in favour of the amendment in Parliament on Tuesday by 297 votes to 110.
The controversial Bill itself was passed at report stage by 276 votes to 231. It has been met by strong opposition because of concerns about its impact on the right to protest, free speech and police powers.
The amendment makes it illegal to interfere "with any person's decision to access, provide, or facilitate the provision of abortion services in that buffer zone" and is punishable by up to two years in prison.
The Public Order Bill is expected to pass all its stages in the Commons and Lords.
Speaking against the amendment in Parliament on Tuesday, Carla Lockhart MP said that existing laws already ensure women are not harassed or intimidated outside abortion clinics.
She shared the story of Alina Dulgheriu who received a leaflet outside an abortion clinic and decided to keep her baby, and another woman who was "under immense pressure" but changed her mind on the way to the abortion clinic after a woman handed her a leaflet and told her she was there if she needed her.
"Her conversation with this woman gave her the support and confidence she needed to keep her baby," she said.
Fiona Bruce MP warned that the amendment "contravenes the basic principle of certainty of the rule of law" and targets "people with faith-based views".
"When did it become against the law in this country to pray?" she said.
Noting that MPs often hand out leaflets at election time, she said they would be "aghast" if they were handed a fine or imprisonment for doing so in future.
Sir Edward Leigh MP questioned why Parliament was again debating abortion clinic buffer zones when the Home Office had declared in 2018 that there was no need for them.
He echoed calls for police to "use their current powers appropriately and where necessary" when dealing with any cases of harassment outside abortion clinics, instead of being in a "rush to create new laws".
Right To Life UK spokesperson Catherine Robinson said: "Hundreds of women have been helped outside abortion clinics by pro-life volunteers who have provided them with practical support, which made it clear to them that they had another option other than going through with the abortion.
"This passing of this amendment means that the vital practical support provided by volunteers outside abortion clinics will be removed for women and many more lives will likely be lost to abortion."
Alithea Williams, Public Policy Manager at the Society for the Protection of Unborn Children, said, "This is a black day for democracy and basic civil liberties. Ordinary, peaceful citizens now risk substantial jail time for the simple act of praying in public, and offering help to women in need.
"Parliament has literally just criminalised compassion.
"This is not just an outrageous assault on civil liberties, it removes a real lifeline for women. Many children are alive today because their mother received help and support from a compassionate pro-life person outside a clinic.
"Many women feel like they have to choice to have an abortion, and pro-life vigils give them options. Now their choices have been taken away."