Women's rights have emerged as a key campaign issue ahead of Sunday's election in Poland.

With the number of undecided female voters twice as high as men in most age groups, according to a Batory Foundation report, sociologists say the opposition's success in galvanizing them could tip the scales.

Political scientists say massive protests that swept through Poland over the abortion ban in recent years may motivate some female voters to support the opposition, but may also have convinced others their voice doesn't count.

A number of campaigns have been launched in recent weeks encouraging women to cast their ballots on Sunday.

"We've been silent already. We will not be quiet anymore," said the Wschod Foundation, which launched the campaign last week to mobilize female voters.

Since winning power in 2015, the Law and Justice (PiS) party has ended state funding for IVF and enforced a prescription requirement for emergency contraception, as well as launching a universal child benefit and cash incentives for women to have at least four children.

PiS says it aims to boost fertility rates and support families while pushing back against liberal values that clash with Poland's Catholic heritage.

PiS' main rival, Civic Coalition (KO) says it will seek legislation to allow for abortion up to 12 weeks without limitations if it wins, in a major turnaround for the party which has shied away from picking a stance on the issue for years.

Fertility rates in Poland fell to the lowest since World War Two this year. Activists say that's in part because women are scared of having children following a handful of cases when pregnant women died of sepsis in hospitals as doctors waited for the fetus' heart to stop beating.

Polls show PiS is likely to win but its support has waned, in part because of its record on women's rights and the rule of law. Some surveys show the mainstream opposition could form a majority government even if PiS is in first place.