Immigrants to Canada will have to keep taking an oath to the Queen after the nation's top court refused to hear a challenge to the citizenship requirement.

The decision by the Supreme Court leaves intact an Ontario Court of Appeal ruling.

At issue is a provision in Canada's Citizenship Act that requires would-be citizens to swear to be "faithful and bear true allegiance to Queen Elizabeth the Second, Queen of Canada, her heirs and successors".

The Queen is titular head of state because Canada is a member of the British Commonwealth of former colonies.

Long-time permanent residents Michael McAteer, Simone Topey and Dror Bar-Natan challenged the law because they do not want to pledge allegiance to the monarchy.

Informed of the Supreme Court decision that ends the battle, Mr McAteer, 81, of Toronto, said he was disappointed, but not surprised.

"It's been a long haul," said the staunch republican who came to Canada from Ireland 51 years ago. "(But) I feel the same: if the oath stands, then I won't take Canadian citizenship."