Pro-life MPs are being urged to speak out against legislation that will impose buffer zones around abortion clinics nationwide.
The buffer zones are proposed in an amendment to the Public Order Bill, which returns to the House of Commons this week.
The amendment was introduced by Stella Creasy MP and passed by MPs last October.
The wording was then amended by Baroness Sugg in January but only to bring the provisions into compliance with human rights laws.
The amended version makes it an offence to engage in any act which has the effect of "influencing any person's decision to access, provide or facilitate the provision of abortion services", and carries the threat of an unlimited fine.
It was backed overwhelmingly by MPs despite concerns around free speech, the risk to vulnerable women, and the threat of criminalisation for praying or offering support.
The Society for the Protection of Unborn Children (SPUC) is urging people to write to their MP asking them to speak out against buffer zones when the Bill returns to the Commons on 7 March.
SPUC's Public Policy Manager, Alithea Williams, called the amendment an "outrageous assault on 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.
"Buffer zones also remove 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."
She added, "We cannot let this illiberal and cruel measure pass without protest."
Pro-lifers are already feeling the effects of buffer zones in place around clinics in some cities. Last month, a Catholic priest, Fr Sean Gough, and pro-life volunteer, Isabel Vaughan-Spruce, were cleared in court after being charged by police with "intimidating service-users" for praying silently inside an abortion clinic buffer zone in Birmingham.
