“NO POLICE state”, demanded one placard. “Freedom not feardom”, read another. Thousands of Canadians brandished such signs on March 14th in protests against Bill C-51, new anti-terrorism legislation proposed by the Conservative government. Stephen Harper, the prime minister, is betting that the demonstrators represent a vocal minority, and that a tougher stance on security will help him win October’s general election. He is probably right. But C-51, though not completely misguided, is flawed.

Since taking office in 2006 the Conservatives have given the security services more power, lengthened sentences for existing terrorism offences and introduced new ones, such as leaving Canada to commit acts of terrorism. C-51 continues this approach. It would make it a crime knowingly to advocate or promote terrorism “in general”. The Canadian Security Intelligence Service (CSIS), which until now has merely collected intelligence, would gain the power to act on it to disrupt potential terrorist activity. Government agencies would be able to share information about individuals more easily.

All this is fine with most Canadians, still traumatised by two “lone wolf” assaults last October in which two soldiers were killed and parliament was attacked. Mr Harper is eager to talk about something other than the economy, which has been hurt by low oil prices. The Liberal Party, which hopes to unseat him in the election, backs the bill with reservations. Only the left-leaning New Democratic Party, the largest opposition party in parliament, is opposed to it outright.

But Edward Snowden’s revelations of mass surveillance by the United States’ National Security Agency (NSA) have alarmed some Canadians. The proposed law seems to bring the peril home. All Canadians, not just terrorists, could be monitored by intelligence agencies, and the government could keep the information they collect forever, complains the privacy commissioner, an agent of parliament.

Civil-liberties watchdogs warn that the vague phrase “in general” invites restrictions on speech—unnecessarily. Already it is an offence to incite, threaten or counsel the commission of terrorist acts. CSIS would gain the power to apply for special warrants that would allow it to contravene Canada’s charter of rights and freedoms. That would put judges in the position of sanctioning unconstitutional behaviour, civil libertarians fret.

The loudest objections are to what is not in the bill: parliamentary oversight of the security services. Unlike security agencies in the United States, Britain and Australia, Canada’s are not subject to scrutiny by the legislature. A committee composed of five part-timers, appointed by the prime minister, hears complaints about CSIS. It is not widely respected; a former chairman has been jailed on suspicion of fraud. Of the 17 agencies that will now share information on ordinary Canadians, 14 are not subject to independent oversight, says the privacy commissioner.

Some parts of C-51 make sense. It would bring Canada’s standards on preventive detention into line with those of Britain, France and Germany, says Christian Leuprecht of the Royal Military College. But even backers concede that the bill is badly worded and that it is a mistake to expand security agencies’ powers without better monitoring.

Stronger supervision by parliament would placate many of the bill’s critics. Mr Leuprecht suggests a sunset clause forcing parliament to review the legislation after a set period. But the Conservatives, with majorities in both houses of parliament, rarely accept amendments. Fearful Canadians will be a little less free.