Poland's parliament on Thursday will open a long-awaited debate on liberalising abortion laws in the majority Catholic country, with splits in the ruling coalition suggesting an uncertain outcome.

Women's rights were rolled back during the eight-year rule of the previous right-wing Polish government, with the tightening of already strict abortion laws sparking mass rallies nationwide.

The country of 38 million has some of the strictest anti-abortion laws in the European Union, allowing it only if pregnancy results from sexual assault or incest, or if it threatens the life or health of the mother.

Elections last October yielded a pro-EU government coalition comprising the Civic Coalition of Prime Minister Donald Tusk and the Third Way and Left groupings.

Tusk's party and the Left have pledged to legalise abortion, but the other coalition members are divided.

Bills that would grant more reproductive rights have been stuck in parliament for months, prompting frustration and anger among many women and rights groups.

A six-hour debate is now scheduled to start on Thursday afternoon on a bill to legalise abortion until the 12th week of pregnancy, submitted by Tusk's Civic Coalition, and three other proposals by its coalition partners.

But the outcome is uncertain as some coalition lawmakers are reluctant to back the legislation in a vote scheduled for Friday.

And even if parliament approves the reforms, they would still need to be signed into law by President Andrzej Duda, which the conservative Catholic ally of the conservative PiS party in the opposition is unlikely to do.

- First hurdle -

"Bills of similar content have been discussed in the parliament many times over the past 30 years but none of them was ever forwarded for further committee proceedings," Krystyna Kacpura, head of the Federation for Women and Family Planning, told AFP.

Tusk, a former EU chief and the arch-foe of the right-wing PiS party previously in power, said he hoped lawmakers representing his coalition would allow the legislation to clear the first hurdle.

"There are many indications that this will be the case," Tusk told reporters on Tuesday.

But lawmakers from the conservative PSL farmers party, part of the Third Way coalition grouping, have expressed reluctance at easing abortion restrictions and some have already said they will not back the bills.

"I will vote against," the PSL's Marek Sawicki told TOK FM radio, though he did not say how many of the party's fellow lawmakers would follow suit.

Tusk's coalition controls 248 of the 460 seats in the parliament's lower chamber, with the PSL holding 32 seats within the bloc. A majority requires 231 votes.

- Presidential obstacle -

Abortion assistance is also outlawed in Poland, with activists and doctors who help with the procedure risking jail.

Last year, an abortion rights activist, Justyna Wydrzynska, was found guilty of providing a pregnant woman with abortion pills, the first such case in the country. She was sentenced to community service.

According to the latest opinion poll by the Opinia24 agency, 50 percent of Poles were in favour of liberalising abortion laws, while 41 percent said they would keep the current rules.

But getting any new legislation past Duda, the PiS ally, will be a challenge.

Last month, Duda vetoed legislation on prescription-free emergency contraception for girls and women aged 15 and over, citing his will to "respect constitutional rights and the standard of health protection for children".

The government has said it will bypass the veto by allowing pharmacists to provide morning-after pills.