National debate is raging over the Liberal government’s plan to reform Canada’s electoral system without a referendum. A slap in the face to voters, many have said. But the voters can be ignored, at least until 2019. More problematic for the Liberals: Their plan is also a slap in the face to the Supreme Court of Canada, which less than two years ago reiterated that fundamental constitutional reform can proceed only with broad provincial consensus.

As the Harper government was so often reminded, Parliament ignores the Court’s prerogatives at its peril. Any attempt by the Liberal majority to unilaterally push through dramatic reform such as proportional representation or preferential balloting would thus be not just politically treacherous, but also legally futile.

That conclusion flows from two important legal principles. First, unlike many other jurisdictions, Canada has no single comprehensive constitutional text. Our Constitution embraces a far-flung collection of imperial and Canadian statutes, conventions, and unwritten principles. It is not limited to a particular text — or even text itself. Historical traditions, including what the Court has called “fundamental constitutional tenets upon which British parliamentary democracy rested,” are at the foundation of our constitutional order.

Second, no single parliamentary majority can alter that foundation alone. Foreign tin-pot tyrants routinely amend constitutions to augment their own powers, but the stability of our democracy precludes willy-nilly revision. Instead, changes to what the Supreme Court has termed our “constitutional architecture” can be achieved only through the more onerous amendment process specified in the Constitution Act, 1982. And for changes that implicate provincial interests, that process demands that the provinces “have a say;” no level of government can unilaterally change the nature of our constitutional institutions.

The Supreme Court famously applied these principles in its reference decision on Quebec secession, ruling that Quebec could not lawfully secede by a bare majority vote. Canada’s Constitution includes unwritten yet foundational principles, the Court explained, such as democracy and the rule of law, none of which can be overridden by “simple majority rule.” And the Court reiterated these constraints in rejecting the Conservatives’ proposal to reform the Senate. The Senate is a basic institution of Canadian democracy, and changes to its essential features could not be unilaterally imposed by the Harper majority. Indeed, “whether or not the letter of the constitutional text is modified,” the Court warned, changes to our constitutional architecture demand broad national consensus.

If these principles precluded the Conservatives from legislating the election of Senators — and even relatively minor reforms, like limiting appointed Senators to fixed terms — surely they also prevent the Liberals from fundamentally reshaping the way we select our principal democratic representatives in the Commons.

The core structure of our electoral system is constitutionally entrenched. Our framers adopted a “Constitution similar in principle to that of the United Kingdom.” They modelled our House of Commons on the one across the pond, whose members have for hundreds of years been chosen, not through proportional representation or preferential balloting, but by constituents in distinct geographic districts. Indeed, Canada’s founding document expressly assigned to each province a fixed number of “electoral districts,” each entitled to return “one member” to the House. This “constitutional architecture” plainly presupposes district-based elections. And the first-past-the-post methodology for those elections has determined the composition of our House of Commons, without deviation, since Confederation.

This is not to say that our electoral system is impervious to reform. But such a basic part of our constitutional order cannot be modified by the federal government acting alone. Like the secession of a province or the Conservatives’ Senate reforms, radical changes to our electoral system clearly engage provincial interests. The strength and composition of provincial delegations in the House of Commons could shift dramatically under a reformed electoral system.

The issue here is not the desirability of electoral reform, but respect for our constitutional order. The status quo may not be the best system, or the most democratic. Neither is appointing senators more democratic than electing them. But our constitutional framers dictated certain mechanisms for distributing political power. They did so for good reasons. To allow a one-off parliamentary majority to unilaterally alter these foundational rules of the political game would be fraught. As the Chief Justice of the United States recently observed: “those who govern should be the last people to help decide who should govern.”

The Liberals were critical of the previous government both for its relationship with the provinces and with the Court. Now that they are in power, they should take their own advice and respect their constitutional counterparts.

Yaakov Roth is a former law clerk for the U.S. Supreme Court and now practices law in Washington, DC. Jonathan Roth is a former law clerk for the Ontario Court of Appeal and now practices law in Toronto. The views expressed here are their own.