MPs are braced for a highly-charged showdown over plans to bar abortion providers from giving advice to pregnant women.
In the first debate on the controversial issue since the general election, the House of Commons is set to vote on a cross-party amendment to the Health and Social Care Bill.
Tory backbencher Nadine Dorries and Labour's Frank Field want to prevent non-statutory abortion providers such as Marie Stopes and the British Pregnancy Advisory Service from offering counselling.
Ms Dorries says that, because they receive money for carrying out terminations, the organisations have a vested interest.
However, MPs are expected to reject the move in a free vote, with the bulk of the Labour Party and Liberal Democrats lining up against it.
All three main party leaders have indicated they oppose the amendment - although David Cameron may not be in Westminster for the division following prime minister's questions.
The premier is said to be sympathetic to the need for more advice for women but is concerned about existing providers being shut out.
Tory Health Minister Anne Milton has emailed MPs saying she and her colleagues at the Department of Health will also be voting against the amendment.
The last time parliament voted on an abortion question was May 2008, when MPs decided to keep the upper time limit at 24 weeks.
On that occasion Mr Cameron supported an unsuccessful amendment by Ms Dorries to reduce the level to 20 weeks.