At their weekend convention in Halifax, the Conservative Party of Canada approved a resolution to “enact legislation which will fully eliminate birthright citizenship in Canada unless one of the parents of the child born in Canada is a Canadian citizen or permanent resident of Canada.” In a subsequent statement, Conservative Leader Andrew Scheer said the measure was designed to “end birth tourism.”

This, more than almost any other Tory proposal, spurred immediate condemnation from opponents. NDP Leader Jagmeet Singh, for one, called it a policy of “division & hate.”

Below, a quick guide to Canada’s somewhat unique policy of granting automatic citizenship to every baby born within its borders.

Most of the world does not grant automatic birth citizenship

If a French woman goes into labour while changing planes at Pearson International Airport in Toronto, the child automatically receives lifetime Canadian citizenship. Canada extends unconditional citizenship to anyone born within its borders under a legal principle known in Latin as “jus soli” (law of the soil). Conversely, if a Canadian woman goes into labour while changing planes at Paris-Charles De Gaulle airport, the child gets nothing except perhaps a decorative French birth certificate. This is generally the law across all of Europe, Asia, Africa and Oceania: A child’s nationality is determined based on the citizenship or residency of its parents rather than the flag flying over the maternity ward at the time. There are exceptions. Germany introduced qualifications into its citizenship law after whole Berlin neighbourhoods started to fill with German-born Turks unable to obtain citizenship. And, in Australia, a child born to two stateless parents may be eligible for a special form of jus soli.

… but most of the “New World” does grant it

Unless they’re the children of diplomats, babies born in Brazil are automatically Brazilians. Mexico confers citizenship on anybody “born in the territory of the Republic, regardless of the nationality of their parents.” Argentina not only extends automatic citizenship to Argentinian babies, but to the babies of Falkland Islanders. All across North and South America, jus soliis the recognized law of the land. There are clerical reasons why this is probably the case: The Americas are full of immigrants and it saves a lot of paperwork if the only prerequisite for citizenship is a birth certificate. The United States didn’t explicitly recognize jus soli until the Fourteenth Amendment in 1868, when it was adopted largely as a means of extending citizenship to millions of slaves freed by the Civil War. Even if the U.S. and Canada dwell in a hemisphere where jus soli is the norm, however, they remain unique among developed countries in that they’re the only ones to confer automatic citizenship.

A whole bunch of people are not aware that they are Canadians

Despite being born in a Calgary hospital, Texas Sen. Ted Cruz expressed confusion when he ran for U.S. president in 2016 that Canada recognized him as one of its own. “Because I have never taken affirmative steps to claim Canadian citizenship, I assumed that was the end of the matter,” he said. Australian Sen. Larissa Waters had to resign last year after she discovered that her Winnipeg birthplace made her a dual citizen, something forbidden for Australian legislators. “It is with great shock and sadness that I have discovered that I hold dual citizenship of Australia and Canada,” Waters said at the time. Fortunately, the Canadian government now maintains an online quiz, Am I Canadian?, in which foreign residents can discover whether maybe they too have been a secret Canadian this whole time.

Jus soli used to be the law across the British Empire

When John A. Macdonald’s family moved from Scotland to Upper Canada in 1820, they didn’t need any special immigration papers. At the time, the rule was that anybody born on a British ship or on British-controlled soil was a “subject” of Queen Victoria and could thus travel anywhere that flew the Union Jack. This policy remained in place well into the 20th century, when the British Nationality and Status of Aliens Act ascribed de facto citizenship to “any person born within His Majesty’s Dominions” — which then included Canada, Australia and New Zealand, among others. The infamous 1914 Komagatu Maru incident, in fact, was at root a dispute over the meaning of “British subject.” The 376 passengers from British India maintained that as fellow British subjects, they should be allowed free passage into any corner of the British Empire. Nevertheless, Canada barred entry to Komagatu Maru passengers on a shipping technicality designed to shun Indian immigration. In 1981, the U.K. did away with jus soli, decreeing that even children born in the British Isles couldn’t be British without at least one parent who was a U.K. permanent resident.

The Tories have proposed axing birthright citizenship before

In 2012, then-minister of Citizenship and Immigration Jason Kenney explicitly proposed phasing out Canada’s policy of jus soli, calling it an outdated relic from the age of steam. “With today’s inexpensive and rapid modern travel, someone can fly in for a couple of weeks, have a child and fly out, and otherwise never actually live in the country and have no intention of doing so,” he said at the time. Kenney was reacting to the growing issue of “birth tourism”: A cottage industry of foreign women having their children in Canada in order to provide them with future Canadian citizenship. A leaked report from Kenney’s ministry estimated that there were fewer than 500 “birth tourists” — a fraction of Canada’s total 360,000 births. Nevertheless, in 2016, a B.C. government report obtained by Postmedia identified at least 26 “birth houses” in the province catering to non-resident women. A Postmedia analysis also found that one in five births at Richmond Hospital were to non-resident mothers.

… And so have the Liberals

In 1998, the citizenship and immigration minister at the time, Lucienne Robillard, suggested it was time for Canada to debate an end to jus soli. The issue then wasn’t birth tourism, but a court decision in which immigration officials had been unable to deport a Toronto woman because it was viewed as violating the rights of her two Canadian-born children. Robillard ultimately dropped the proposal, in part because of concerns that it would inaugurate a new demographic of “stateless” Canadians. In 1999, she even praisedjus solias part of the “Canadian humanitarian tradition.”