The Oakland City Council has suddenly declared that Mayor Libby Schaaf’s “Children’s Initiative” passed in last month’s election even though it failed to receive the required two-thirds voter approval.

The seemingly unprecedented decision to effectively move the election goal posts closer after the ballots were counted constitutes a stunning breach of trust with the voters.

This decision is headed to court, where it should be stopped. Voters were told by the city attorney before the election that Measure AA required two-thirds approval. It fell short with 62.5 percent support. Suddenly, the council says it only needed majority backing. The time to make that argument was before the campaigning began.

Measure AA is a 30-year, billion-dollar measure to provide early childhood education as well as mentoring and financial assistance to increase college accessibility.

The initiative would levy a $198 annual tax on single-family houses in the city and $135 on apartments and residential condominiums. Commercial properties would be taxed at multiples of the single-family-house rate depending on size.

The measure was well-intentioned but horribly drafted, with no clear budget or plan for achieving its goals. Which probably helps explain why it fell more than 5 percentage points short of what was needed for approval in a city that rarely turns down tax increases.

Rather than do the right thing – bring back to voters a measure with an explicit plan and budget, and proper accountability and safeguards – the City Council decided Tuesday to simply declare that Measure AA had passed.

It suddenly claimed that voter support surpassing 50 percent was enough. This even though City Attorney Barbara Parker clearly stated in the voter pamphlet that the measure required two-thirds approval. She said it twice, in the official summary of the measure and in the impartial analysis.

But the council ignored that. The vote was 6-1, with only Councilwoman Lynette Gibson McElhaney recognizing that the rules laid out at the start of an election matter. Councilwoman Desley Brooks was absent.

As for the mayor, who only votes in case of a tie, Schaaf has ducked questions about whether she supports this end-run on the election process, although we’re told she encouraged it.

Worse, the council took the action without proper public notice, in apparent violation of the state’s open-meeting law requirement under the Brown Act.

The meeting agenda simply indicated that the council intended to adopt a resolution officially declaring the results of the Nov. 6 election. This is normally a ministerial act.

There was no indication that the council would consider overturning the results. Apparently now recognizing that its vote might have been illegal, the council plans to reaffirm it at a special meeting Friday afternoon.

There is a rational legal argument for why the measure might have required only majority support. But it should have been considered before the voting and campaigns commenced.

In a 2017 ruling, the state Supreme Court seemed to suggest that local initiatives like Measure AA put on the ballot through a signature-gathering process require only majority approval, not the two-thirds necessary if a governmental body like the City Council were to place an item before voters.

The decision upended 20 years of generally accepted thinking about how to apply two seminal statewide initiatives restricting tax increases: Proposition 218 in 1996 and the original Proposition 13 property tax-cutting measure of 1978.

But the case had to do with election timing, not the vote threshold, so some have wisely cautioned against an overbroad interpretation until the high court provides clarity.

Meanwhile, San Francisco voters this year passed three measures similar to Oakland’s Measure AA using the majority threshold. Two of those measures are currently tied up in litigation.

But there’s a big difference between the San Francisco and Oakland measures. In San Francisco, voters were told in advance in the ballot material that the threshold would be 50 percent.

In Oakland, Parker determined that Measure AA would require two-thirds approval. Those were the rules of the game. If backers of the measure wanted to challenge that, they had their opportunity before the ballot pamphlet was published — and before proponents and opponents conducted their campaigns with the two-thirds threshold as the target.

There are standard procedures for review and legal challenges of the ballot wording and material. Backers of the measure, including Schaaf, and the City Council had an opportunity to do so and did not act.

To change the rules of the game now – after the ballots are counted – is a deplorable undermining of the election process.