A top state Democrat’s effort to shame Gov. Cuomo into rejecting the Independence Party’s endorsement is rooted in escalating Democratic unhappiness with Cuomo’s courting of Republicans in Albany and on Long Island, The Post has learned.

Cuomo, for his part, is “furious’’ that former state Democratic Chairman Jay Jacobs has “put him in an untenable political box’’ by urging him to dump the backing of the anything-but-independent, scandal-scarred, Independence Party, according to one of the state’s best-known Democrats.

Jacobs, a businessman, current Nassau County Democratic chairman, and state chairman under Gov. David Paterson, stunned Cuomo and other top Democrats last week by publicly urging Cuomo and GOP gubernatorial hopeful Rob Astorino to decline Independence support, a move that would drive the party out of existence.

Jacobs told The Post, “Democratic leaders across the state overwhelmingly agree with me that the Independence Party is a political cesspool.’’

While Cuomo, who was elected with Independence backing in 2010, claims to back political reform, his refusal so far to even respond to Jacobs’ call “has exposed the governor’s hypocrisy and, frankly, he doesn’t know what to do,” the well-known Democrat said.

The Independence Party, which thousands of New Yorkers have joined by accident thinking they were enrolling as “independent’’ voters, is widely seen as a “transactional’’ party with its endorsement up for sale, especially to the Senate Republican’s campaign committee, with which Jacobs regularly battles on Long Island.

Cuomo, seeking a big re-election victory, has been aggressively courting Nassau Republicans, including Senate GOP Leader Dean Skelos and County Executive Edward Mangano, who many Nassau Democrats say Cuomo helped to win re-election last year.

What’s more, former US Sen. Alfonse D’Amato, a lobbyist with interests before Cuomo’s office and a key figure in Nassau GOP and Independence politics, has endorsed Cuomo and advises him on Long Island politics.

Cuomo and many other Democrats were stunned by Jacobs’ public action not only because the governor was planning to accept Independence backing but because Jacobs’ language suggested that Cuomo either agree to dump the party’s backing or be viewed as corrupt, Democratic insiders agree.

“For anybody that takes ethics in government as an important issue, this is a no-brainer,’’ Jacobs said when asked about what he expected Cuomo to do.

Late last week, Cuomo unleashed Democratic attacks on Astorino, the Westchester County executive, for having run in the past with Independence support and for giving the party some campaign contributions.

But Jacobs disagreed, and came to Astorino’s defense.

“Aren’t sins absolved once you find Jesus?’’ quipped Jacobs, noting that Astorino has agreed not to seek Independence support.

“The bottom line is that Astorino is doing exactly what I would have hoped he would do on this issue.’’

Many of New York City’s most powerful Democrats, furious over what they say is Cuomo’s humiliating treatment of Mayor de Blasio, are privately cheering on Jacobs.

The Independence Party can keep its status as a legally recognized political party only if its gubernatorial candidate receives at least 50,000 votes in November.