Opposition leader Donald Tusk told supporters that political “change for the better is inevitable” in Poland as he opened a massive march Sunday to try to boost his political coalition’s chances of unseating the country’s conservative government in an upcoming parliamentary election.

“No one can stop this force; this giant has awoken,” Tusk told huge crowds gathered in the center of Warsaw two weeks before the Oct. 15 election. “Let no one among the ruling team have any illusions: This change for the better is inevitable.”

His Civic Coalition is vowing to mend ties with the European Union, which has had strained relations with Poland during the eight years the Law and Justice party has governed the country. Tusk spent five years as president of the European Council after serving seven years as Poland’s prime minister.

The four-party coalition also has pledged to pursue more tolerant policies than the nationalist government led by Law and Justice.