SINCE Canada enacted a rule in 2011 requiring veiled women to reveal their faces during public citizenship ceremonies, the country has sworn in 680,000 citizens. Just two have refused to comply. This seemingly marginal issue has come to the fore in campaigning for the national election to be held on October 19th. It could well affect the outcome.

When and where women wear a niqab, which covers all but the eyes, became an issue last month when the Conservative government said it would appeal to the Supreme Court a lower court’s decision that the rule contravenes the Citizenship Act. This requires judges to allow the greatest possible religious freedom when administering the citizenship oath. The fuss is a godsend for Stephen Harper, who hopes voters will re-elect him for a fourth term as prime minister—despite their fatigue with his ten-year rule and a weak economy. “When you join the Canadian family in a public citizenship ceremony it is essential that that is a time when you reveal yourselves to Canadians,” he declared.

Canada’s 1m Muslims are dismayed. Although hate crimes in general are declining, those targeting Muslims are not. In the past week, a pregnant woman wearing a headscarf in Montreal was knocked down by two teenagers. Another wearing a niqab in Toronto said she was assaulted. Politicising the niqab is “unbelievably dangerous”, said Calgary’s mayor, Naheed Nenshi, who is a Muslim.

It also puts Mr Harper’s rivals, the Liberal leader Justin Trudeau and Thomas Mulcair, leader of the left-leaning New Democratic Party (NDP), in an awkward spot. Both sympathise with people who find the niqab off-putting but think the unveiling rule infringes freedom of religion. It serves no practical purpose. Veiled applicants must reveal their faces to a citizenship official before taking the public oath. Police and intelligence services vet would-be citizens. The opposition accuses the government of stirring up anti-Muslim sentiment.

Public opinion is with the prime minister. Canadians are famously tolerant, but 80% think women should unveil at citizenship ceremonies. Conservatives are keeping the issue alive. Last week two ministers promised to set up a telephone tip line for people to report violations of the “Zero Tolerance for Barbaric Cultural Practices Act”, which outlaws honour killings, polygamy and child marriage. On October 6th Mr Harper said he would consider barring civil servants from wearing the niqab. He wants the unveiling rule to become a law.

The controversy is especially damaging to the NDP, whose political base is in Quebec. The French-speaking province has had wrenching arguments about how far the state should go to accommodate religious minorities. Support for an unveiling law is even higher in Quebec than in Canada as a whole. The province is considering a law that would ban the niqab in government offices. The separatist Bloc Québécois, which only fields candidates in the province, has aired anti-niqab adverts.

This is costing the NDP votes. It now lags well behind the Conservatives and Liberals in the national race. On October 4th Mr Mulcair appeared on a popular Quebec talk show in a segment entitled “tempête dans un niqab” (tempest in a niqab) to defend his position. Even small storms can do a lot of damage.