MPs are being urged to vote in favour of lowering the abortion time limit from 24 weeks to 22 in light of improved survival rates for premature babies.
Right to Life UK said that a 24-week abortion limit "is now beyond the point when many babies survive" and that lowering it would bring the UK more in step with more European Union countries.
Many EU countries have a 12-week limit - the same point at which the NHS describes unborn babies as "fully formed".
The last time the abortion time limit was lowered was in 1990 when it was brought down from 28 weeks to 24 weeks.
Right to Life said there was a "contradiction at the heart of our abortion law" which means that "a baby at 22 or 23 weeks' gestation could be born prematurely and have a dedicated medical team provide expert care to try to save his or her life, while another baby at the same age could have their life deliberately ended by abortion in the same hospital at the same time".
A historic vote on the abortion time limit is expected to take place next month after a cross-party group of MPs tabled a landmark amendment to the government's Criminal Justice Bill.
The group is led by Caroline Ansell MP who said it was time the law was brought into line with medical advances.
"The increase in survival rates for babies born at 22 and 23 weeks gestation is one of medical science's great success stories in recent years," she said.
"More and more babies born at these ages are able to survive thanks to the hard work of neonatal teams.
"As in 1990, when our laws were last changed to reflect similar increases in survival rates, it is time our abortion time limit was updated.
"Our current time limit is an outlier compared with our European neighbours and my hope is this amendment will command widespread support across the House."
The group of MPs supporting the amendment includes former health minister Maggie Throup, ex-shadow cabinet Labour minister Rachael Maskell, ex-shadow Labour minister Marie Rimmer, ex-Cabinet Minister Sir Jacob Rees-Mogg, and Miriam Cates MP.
