Peaceful citizens are at risk of being branded criminals after a controversial amendment to the Public Order Bill was passed in the Lords this week, a pro-life group has warned.
Amendment 45 will introduce buffer zones banning prayer vigils and offers of help outside abortion clinics nationwide.
The Society for the Protection of Unborn Children (SPUC) called the proposed ban an "outrageous assault on civil liberties".
The amendment put forward by Baroness Sugg was passed by a voice vote.
It makes it an offence, punishable by an unlimited fine, to engage in acts "influencing any person's decision to access, provide or facilitate the provision of abortion services".
SPUC's Public Policy Manager, Alithea Williams, called it a "black day for democracy and basic civil liberties".
"Ordinary, peaceful citizens will now be branded criminals and subject to crippling financial penalties for the simple act of praying in public, and offering help to women in need," she said.
"Parliament has literally just criminalised compassion – and without even voting on it. And that's the point. 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."
One pro-lifer has been arrested and another fined in the last two months near abortion clinics.
Isabel Vaughan-Spruce, Co-CEO of March for Life UK, was arrested in December after allegedly being told by police that she might have been praying silently.
Last month, army veteran Adam Smith-Connor was fined after praying silently for his deceased son near an abortion facility in Bournemouth.
Ms Williams continued: "Thoughtcrime is now very real in the UK. It is very disappointing that peers ignored these warnings and voted for this extreme and cruel legislation."
Catherine Robinson, spokesperson for pro-life campaign group Right To Life UK, said that the amendment was "nothing short of the criminalisation of a particular point of view".
"It makes it illegal to be publicly, and even privately, pro-life in a certain part of the country," she said.
"In all likelihood, this poorly thought-through piece of legislation will be passed by the House of Commons and result in a series of court cases because it is not clear in a case of silent prayer for example, whether an individual is breaking the law or not."
She added, "This legislation is an instance of the abrogation of responsibility since it will ultimately be the decision of a particular judge to set the precedent for the correct interpretation of the law."
