Poles will elect a new parliament on Sunday as the governing socially conservative Law and Justice party seeks to maintain its outright majority in the lower house while opposition parties hope for an upset and a broad anti-PiS government.

Poles select 460 lawmakers for the Sejm, the lower house and main legislative body, as well as 100 members of the Senate, an oversight and review chamber.

PiS was the clear leader in opinion polls ahead of the Sunday ballot and is expected to win between 40 and 49 per cent of the vote, which could potentially give it an outright majority in the lower house.

The main opposition forces - the centrist Civic Coalition (KO), the Democratic Left Alliance (SLD) and the Christian Democrat agrarian Polish People's Party (PSL) - hope in turn that their combined support can top that of PiS, allowing them to form a coalition government.

The common denominator of the opposition is a pro-EU stance and a pledge to undo controversial broad institutional reforms introduced by PiS in the last four years, including in the judiciary, which put the country at loggerheads with the European Commission.