Both sides have deployed posters and billboards to get their message across
Voters in Berlin are preparing to go to the polls to decide whether children should have a choice between classes in secular ethics or religion.
Sunday's referendum has been organised by Berliners from the city's religious communities, including Muslims.
Ethics classes have been compulsory in Berlin schools since 2006. But in most of the rest of Germany pupils have a choice between religion and ethics.
Opponents say that any changes to the curriculum will be divisive.
Berlin introduced ethics classes after the "honour" killing of a Muslim woman by her husband, a shocking incident in a city that is often seen as a multicultural success story.
Before the change, children in the city could choose to take voluntary religious education classes, but these were poorly attended.
The ethics classes were intended to instil a sense of shared secular values in children, whatever their personal religious beliefs.
Classes in religion could only be taken outside of school hours.
Now, an alliance of religious campaigners and parents' groups says the attendance rate for these lessons has dropped even further, by up to two-thirds, and that action must be taken.
Ethical versus religious education: Berliners will decide on Sunday
The Pro-Reli campaign - "Reli" being the colloquial shorthand for religious lessons - persuaded 265,000 people to sign a petition, which led to the referendum.
And German Chancellor Angela Merkel has added her voice to the debate. She told a meeting of her Christian Democratic Union party on Friday that she supported the Pro-Reli campaign.
"I hope that many citizens come out in support of it," she said.
Berlin's ethnic mix includes the largest Muslim community in Germany, and all eyes are now on them to see how they vote on Sunday.
Many people from the community support the proposed change in the law, hoping that if it is successful, Islam will find its way into the official school day.
The Turkish-Islamic Union for Religious Affairs (Ditib) is one such supporter. Their spokesperson Ender Cetin argues that fostering a knowledge of officially-sanctioned Islam can help prevent young people from being lured into radicalism.
"It's important that schools have enlightened Islamic lessons, and that we avoid unofficial Koran lessons in backyards."
Julia Sebastian, a spokesperson for Pro-Reli, says the campaigners just want what children in most of the rest of the country have.
"We were pretty surprised we got so many signatures to force the referendum," she said.
She is not surprised that Ditib is supporting the motion.
"They feel this is a much better tool for integration. There is a certain fear about Islam entering schools, but I'm not afraid of it.
"I think the government can deal with radicalism better by having Islam in schools."
But opponents of the change argue that focusing on religious rules could lead to young people missing out on shared secular values.
Germany's Left Party is among those campaigning for a "No" vote. Their vice-president in the Bundestag - parliament's lower house - is Petra Pau, a former teacher. She accused Catholics of trying to lead a new crusade.
At least 600,000 Berliners must vote for the referendum to even be valid and a majority of those must support the change for it to go through.
To that end, both sides have put up posters around Berlin, many of which have been defaced.
It is a sign that feelings are running high in a classic case of secularism versus religion.