Assemb. Todd Kaminsky, the Democratic candidate for the seat of former State Senate Majority Leader Dean Skelos, on Tuesday accused his GOP opponent, Christopher McGrath, of “cozying up” to a pro-Common Core group that funded a $1.2 million ad buy in advance of the April 19 special election.

New Yorkers for a Balanced Albany, a political action committee formed by StudentsFirst, a nonprofit that supports charter schools and Common Core standards, spent $1.28 million last week on TV ads and polling against Kaminsky (D-Long Beach), according to State Board of Election records.

The ad, titled “Taxing Todd,” says a Kaminsky victory would allow Mayor Bill de Blasio to control all levers of state government, increasing taxes for Long Islanders.

The PAC spending came a week after Senate Republicans helped obtain $54 million in funding in the 2016 state budget for charter schools statewide — a 3 percent increase.

At a news conference in Oceanside with education activists, Kaminsky accused Senate Republicans of orchestrating a “secret deal” to fund the ads in exchange for the charter school hike. “Advocates for the Common Core ... advocates for charter schools are trying to come down here on Long Island and steal this election,” Kaminsky said.

Senate GOP spokesman Scott Reif called the allegation “slanderous” and said the campaign was legally prohibited from coordinating with outside groups. “Senate Republicans, however, aren’t going to apologize for providing a record level of total funding for Long Island schools,” Reif said.

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McGrath, an attorney from Hewlett, “opposes the implementation of Common Core” and “understands the need to eliminate the unnecessary over testing of our kids and return to local control of our schools,” said campaign spokesman E. O’Brien Murray.

Jenny Sedlis, executive director of StudentsFirstNY, defended the ad. “Albany functions better when one party isn’t in control of everything and our schools perform better when legislators who care about education are in office,” she said.

McGrath’s campaign also criticized Kaminsky for missing Assembly votes Monday on bills addressing obesity education and women’s pay equity. Kaminsky has missed five days in Albany and 28 votes since March 29, the campaign said.

“It’s hypocritical of him to ask for their vote to be their senator, when he can’t show up for work and represent them on important issues as an assemblyman,” said McGrath spokesman Marcus Povinelli.

Kaminsky has an “outstanding” attendance record in the Assembly, said campaign spokesman Evan Thies.

Kaminsky and McGrath are vying for the 9th Senate District seat, which was vacated in December when Skelos was convicted on federal corruption charges. He and his son, Adam, who also was convicted in the case, are appealing.

Laurence Hirsh, an accountant from Valley Stream, is running on the Green Party line.