An estimated 500,000 people from all over Poland marched in an anti-government rally in Warsaw on June 4, turning up the heat of political debate ahead of historic election due later this year.

The march followed intense weeks in Polish politics, marked by the Law and Justice (PiS) government’s missteps, which echoed at home and abroad, and likely fuelled the turnout at the rally, the biggest in Poland’s history since communism.

“You're all here because you have just believed we can win. Democracy dies in silence. As of today, the silence is no more,” Donald Tusk, the leader of the biggest opposition party, Civic Platform (PO), told the crowd, which crammed into Warsaw’s Castle Square.

Tusk originated the idea of the rally a few weeks earlier, sensing an opportunity that holding an anti-PiS protest match on an anniversary of Poland’s historic election of 1989 could boost his party’s momentum in the run-up to the forthcoming election.

But PiS and the ruling party’s ally, President Andrzej Duda, likely caused many people far beyond party affiliations to participate in the rally.

A few days before the rally, Duda signed off on a controversial law that has established a special commission to probe Russia’s influence on Poland’s internal security.

The commission, simply by deciding that a politician’s decisions were made under Russian influence, can bar him or her out from taking public office.

The opposition fears the bill could be an attempt to eliminate Tusk from running in this autumn’s election, using trumped-up allegations served up by the commission.

After a backlash at home and – perhaps more importantly – from the US and the EU, Duda submitted amendments to the law he had only just signed, trimming the commission’s powers.

But the law, dubbed “lex Tusk” in the meantime, triggered a wave of anti-PiS sentiment last seen after the PiS-controlled Constitutional Tribunal virtually banned the right to abortion.

Early signs of a huge turnout coming up were seen at Warsaw metro lines, where people were left out on the platforms as trains calling at stations were too full for them to board.

A tightly packed crowd filled the streets and squares within several hundred metres of the rally’s starting point and only began marching after a two-hour wait.

People held Polish flags and anti-government placards and banners. “PiS = Polexit,” read one, referencing fears that the PiS rule could eventually lead to Poland’s leaving the EU.

“TVP lies,” read another, referring to the government-controlled broadcaster which initially ignored the rally and later painted it as a “march of hatred” serving Russia.

“We are going to win the election and hold [PiS] accountable," Tusk said shortly before the rally dissolved to the tune of “I love freedom,” a Polish hit song from 1990, performed live by contemporary singer Bovska.

Tusk and other opposition parties – whose leaders were also present at the march – have just over four months to ensure their combined result at the polling stations gives them a majority over PiS and the far-right, which the ruling party is said to be eyeing as a potential coalition partner.

PiS averaged 35.5% of support in May polls, ahead of the coalition of PO and smaller parties (known as the Civic Coalition) at 27% and the Third Way – a joint effort by centrist Polska 2050 and agrarians from PSL – at 14.5%.

The far-right Konfederacja polled at 11% on average in May, while the Left’s average was 10%.

Simulations show that PiS would only win 190 seats in the 460-seat parliament (Sejm) but could secure the slimmest of majorities, of 231, in a coalition with the far-right.