Women's rights are high on the agenda in Poland, which introduced a near-total ban on abortion in 2021 and where the previous, nationalist government embedded its conservative social values in law during its eight-year rule.

Since winning power in October, Tusk's broad coalition that encompasses left-wing politicians alongside Christian democrats, has already reinstated public funding for in vitro fertilisation and voted to change rules on access to emergency contraception.

But it is struggling to agree on abortion policy, a key focus of Tusk's campaign which tapped into simmering public anger about the tough curbs. Political observers said it was one of the motivations behind a record turnout in the October vote.

"The atmosphere is heated because it is something we differ on among coalition partners," parliament speaker Szymon Holownia, a former Catholic journalist, told reporters on Wednesday.

Holownia's decision in March to postpone a debate on easing abortion laws until after local elections last weekend angered some voters and his leftist coalition partners in parliament.

Under existing laws, abortion is legal in the case of rape, incest or a danger to the woman's health or life, but terminations of pregnancies with foetal defects are banned.

Activists say even legal abortion is often difficult to obtain because doctors and hospital administrators are unsure of the rules or refuse to perform terminations on moral grounds.

Opinion polls show, however, that Poland, a predominantly Catholic country, is shifting away from the Church's teachings and a growing number of voters want more abortion rights. A recent survey by Ipsos said 62% of Poles support the right to abortion until 12 weeks.

Fertility rates in Poland fell to the lowest since World War Two last year. Women's rights campaigners say that's in part because women are fearful of having children following a handful of cases in which pregnant women died in hospital as the result of complications linked to strict abortion rules.

Thursday's debate will focus on three bills, each put forward by one of the three coalition groupings.

Two of the bills would make abortion legal without limitations until 12 weeks of pregnancy.

The other reinstates the right to abortion in case of foetal abnormalities, returning to the situation before a 2020 constitutional court ruling banned such procedures.

It is unclear how long the debates will last on Thursday. It is widely expected that President Andrzej Duda, a conservative ally of the former ruling Law and Justice (PiS) party, will veto any changes to legislation.

"We are very keen to finally start the debate. We've been asking for it repeatedly," Katarzyna Kotula, minister for equality, told Reuters. "This is important to us, but nothing will change quickly."

(Reporting by Anna Wlodarczak-Semczuk, Karol Badohal and Pawel Florkiewicz; Editing by Ros Russell)