Polish voters cast their ballots on Sunday in the second round of the presidential election, marked by a fierce contest that could significantly shape Poland’s future role in the European Union and impact key social issues such as abortion rights.

Polling stations opened at 5 a.m. local time and will remain open until 7 p.m. GMT in this EU and NATO member state, which has been a strong supporter of Ukraine amid Russia’s ongoing invasion.

The runoff pits Warsaw Mayor Rafal Trzaskowski, a 53-year-old pro-European candidate, against nationalist historian Karol Nawrocki, 42, backed by the ruling conservative Law and Justice party led by outgoing President Andrzej Duda.

Recent polls show an extremely close race, with Nawrocki holding 50.1% of voter intentions and Trzaskowski trailing slightly at 49.9%, a margin within the poll’s error range.