If you want to become a Canadian citizen, one of the requirements by federal law (the Citizenship Act) is that you take an oath of allegiance to British Monarchy, currently head by King Charles. It’s a serious requirement, just like the knowledge examinations are (demonstrating adequate knowledge of one of English or French and the responsibilities and privileges of citizenship). Now given the history of the British Empire, there’s understandably people that have issues with the British Monarchy and so these people would not want to take the oath of allegiance to the Crown. One group took the federal government to Court, alleging that the Canadian citizenship requirement of taking the oath is unconstitutional, because it unjustifiably violates their Charter Rights and Freedoms, such as their freedom of expression, religion and equality rights.

The Court analyzed the purpose of the oath given the history and evolution of Canada, and found that the underlying substance of the oath is to pledge allegiance to Canada’s system of government, not to the King as a person. As a result, the Court concluded that oath is simply requiring a person to express agreement with the fundamental structure of the country as is. And that rather than undermining freedom of expression, the oath amounts to an affirmation of the societal values and constitutional architecture of this country, which promote and protect expression. The same considerations apply to the claim that the oath violates freedom of religion (a commitment to the King as a symbol of Canada’s constitution not as a person to be worshipped), in addition to the fact that the oath is secular in wording anyway. Therefore, the oath is not a violation of constitutional rights of permanent residents.

There's also a technical legal issue with this argument, in that it would force a conflict within the constitution itself. Because section 128 of the constitution requires members of parliament to take an oath of allegiance to the crown. The legal principle that the constitution (as other laws) must be read harmoniously, means that the oath has to be interpreted as consistent with the rights and freedoms under the constitution.