Whatever plan the nine-member Public Finance Reform Commission releases soon, the Legislature should reject it — because the panel has sacrificed whatever shreds of legitimacy it had with its nakedly cynical maneuverings.

The most obvious outrage is the out-of-the-blue effort to kill the Working Families Party — via rule changes that few if any legislators realized they were empowering the commission to make.

Yes, we’d love to dance on the WFP’s grave — it’s a pernicious parody of a political party that exists exclusively to serve special interests, mainly public-employee unions. But that doesn’t justify killing it in a backroom deal, as the commission by all accounts stands poised to do.

Officially, the change would just raise the bar for how many votes a party must win on a statewide ballot to retain its guaranteed line in future elections. The bar is now 50,000, but all the numbers floated for the new line are above what the WFP can hope to achieve. (Some targets would also kill the Independence Party, which is also pretty pernicious, and even the Conservative Party, which still stands for some principles.)

You can make a fine policy case for raising the cutoff, as you can for completely ending “fusion voting,” which lets minor parties endorse major-party candidates. (Indeed, we’re on record supporting such a change.) But it’s not supposed to be this panel’s job.

On top of that, the head of the commission that’s poised to kill one party is in fact the head of another one, state Democratic Chairman Jay Jacobs.

It’s plainly obscene that Jacobs is even a member of a commission that’s rewriting campaign and election laws: The conflicts of interest are blatantly huge.

But state lawmakers didn’t notice that Gov. Andrew Cuomo slipped a line into the bill to create the commission that lets his handpicked party boss “serve” on it.

No, Jacobs and other Cuomo-picked members aren’t a commission majority; they have to cut deals with other pols’ picks. But the whole thing still reeks — and will even if they drop the bid to kill the WFP.

Sadly, all manner of supposed “reformers” are likely to get bought off simply because the commission gives them what they want — the “right” limits on private donations and the “right” amount of taxpayer funding, for state political campaigns. Blatant corruption is OK, we guess, when it’s in the name of “cleaning up the system.”

(Meanwhile, Cuomo is busy topping off his campaign coffers before any new limits kick in. Nor is he the only state politician busy collecting fat checks from every possible special interest before new rules kick in.)

Other commission outrages abound: It has met behind closed doors, in defiance of the state Open Meetings Law. Further spitting on the spirit of that law, members are clearly negotiating hot and heavy privately, outside public sessions.

It hasn’t hired a staffer to handle requests for records that are supposed to be public. Its members didn’t even take the Public Officers Oath until more than a month after it began operating — after the legal 30-day mandate for swearing in.

All this guarantees major court challenges to whatever the commission produces, as does the whole constitutionally dubious exercise of handing off tremendous changes in election and campaign law to an undemocratic commission.

Under the enabling legislation, whatever plan the commission releases this month will become law unless the Legislature rushes back to Albany for a special session to nix it. In reality, the whole thing’s sure to wind up in court for months if not years: Judges are still rewriting the product of last year’s similar commission to change the rules on lawmaker’s pay.

More important, this circus is already so tainted — and so far removed from what legislators thought they were authorizing — that any honest lawmaker should be already announcing his or her eagerness to vote to reject the results.

And any honest member of the commission should support a motion to just disband.