Californians didn’t stumble into the two-thirds vote requirement for local special taxes, they chose it — twice.

Proposition 13 (1978) and Proposition 218 (1996) deliberately set a high bar for taxes that are earmarked, so the government has to build broad support before asking residents for more money.

That arrangement worked well for nearly four decades: Local leaders made their case, voters weighed the evidence, and only the proposals with genuine community backing crossed the finish line.

Then came a 2017 California Supreme Court decision involving the city of Upland. While settling a narrow procedural dispute, the justices cracked the very foundation of that taxpayer safeguard.

Their opinion hinted — without squarely deciding — that a tax placed on the ballot by a citizen initiative (rather than by a city council, board of supervisors or other elected body) might escape the two-thirds vote requirement.

Within months, consultants and politicians were scouting for ways to slip new taxes through that opening.

Now the Legislature is poised to turn that hint into law. Senate Bill 512 would let citizens place majority-vote sales taxes on the ballot via initiative to fund public transit. Supporters call the bill a “clarification.”

In actuality, it would lock in a loophole that everyday Californians never approved — and that the court itself never explicitly endorsed.

Why does this matter? Because sales taxes — the favored tool for transportation measures — hit every Californian.

Every time you buy groceries, school supplies or a tank of gas, the sales tax adds to the cost.

Years of inflation spikes have left many families unable to afford the same things they could buy five years ago.

Another half-cent here and a quarter-cent there may sound painless on the ballot, but the extra taxes pile up at the checkout stand.

Sales taxes add to California’s unaffordability crisis — and businesses pay, too, on the equipment they need to expand and hire. Even schools and universities are hit, siphoning dollars away from classrooms.

Defenders of SB 512 say California desperately needs transportation money, but this argument doesn’t justify shortcuts. The current system doesn’t prevent local governments from raising funds, it simply requires that they earn a two-thirds vote — proof that the community agrees the project is worth the cost.

Public opinion polls consistently find that Californians, despite having major political differences on many issues, oppose reducing the two-thirds vote requirement for special taxes.

This was reflected in the results of last November’s election, where Californians soundly defeated a measure that would have reduced the two-thirds vote to 55 percent for taxes needed to repay local bonds that fund housing projects (Proposition 5).

From a legal perspective, California Supreme Court Justices Leondra Kruger and Goodwin Liu both agreed with taxpayer advocates that the vote-threshold portion of the Upland decision rests on the false premise that there is a relevant difference between a tax enacted by a city and a tax enacted by the residents of the city exercising their initiative power.

There is no difference — the tax is collected in the same way, the money is used in the same way, and the taxpayers end up paying more, regardless of who put the measure on the ballot.

California can fix potholes and expand transit without gutting taxpayer safeguards.

Lawmakers should reject SB 512 and instead clarify that all special taxes, however they reach the ballot, still need two-thirds support.

If the court cracked the foundation of our taxpayer protections, the Legislature can shore it up.

Robert Gutierrez is the president of the California Taxpayers Association, the state’s largest and oldest association representing taxpayers.