The largest gun safety group in the U.S. is launching a $500,000 ad campaign in the closely watched Wisconsin state Supreme Court race targeting conservative candidate Daniel Kelly over his stances on abortion rights and guns.

The campaign by Everytown for Gun Safety, the massive gun control nonprofit founded in part by former New York City Mayor Michael Bloomberg, is built around a 30-second television ad that blasts Kelly as “too extreme.” The ad ties Kelly to a “radical anti-abortion group,” claims he “opposed background checks on all gun sales” and points out a 2017 decision it says made “it easier for dangerous people to carry guns in public.”

Details of the ad campaign were provided first to NBC News. Everytown will publicly announce the campaign later Monday.

“Banning abortion. Putting our communities at risk. Dan Kelly is too extreme for our Supreme Court,” the narrator adds.

The 30-second spot will air in the Milwaukee and Madison media markets starting Monday.

Kelly, a former state Supreme Court justice who lost his seat in a 2020 election to liberal Jill Karofsky, authored a decision for the state’s high court in 2017 that barred the city of Madison from banning guns on its public buses under the state’s concealed carry law. That decision was the basis for the claim in the group’s new ad accusing Kelly of making it easier for people to carry guns, Everytown spokesperson Sahil Mehrotra said. Mehrotra added the group based its claim in the ad that Kelly opposed background checks on the NRA’s endorsement of Kelly during his 2020 race.

A spokesperson for the Kelly campaign did not respond to questions from NBC News about Kelly’s views on guns.

The April 4 election between Kelly, the conservative candidate in the officially nonpartisan race, and Janet Protasiewicz, the liberal candidate, will determine ideological control of the court. Protasiewicz is a Milwaukee County Circuit Court judge who has received the endorsement of the Democratic abortion rights group Emily’s List. The winner of the race will be elected to a 10-year term.

The contest has already become the most expensive state Supreme Court race in U.S. history.

Everytown’s ad campaign adds to the massive spending that groups supporting Protasiewicz have so far carried out. Protasiewicz and groups supporting her have heavily outspent Kelly and groups supporting him on ads.

Although the court and its members are technically nonpartisan, conservatives hold a 4-3 majority. With conservative Justice Patience Roggensack retiring, that majority hangs in the balance. There has not been a liberal majority on the court in 15 years, and Democrats see the election as a prime opportunity to change that balance.

Democrats in the state have described the race as the most important one anywhere in the nation this year. They, and outside groups, have focused their messaging heavily on abortion rights — extending a strategy the national party employed last year to help keep the Senate and limit losses in what was expected to be a strong election year for Republicans.

“Dan Kelly wants to make it harder for women to make their own reproductive choices and easier for criminals to get their hands on guns — both of which are terrible for the health and safety of Wisconsinites,” Everytown for Gun Safety president John Feinblatt said in a statement to NBC News, adding that it’s important to “elect state judges who respect the right to take common-sense steps to prevent gun violence.”

The outcome of the court race is certain to impact the future of abortion rights in the state. After the U.S. Supreme Court overturned Roe v. Wade last year, an 1849 state law banning abortion in almost all cases snapped back into effect. Gov. Tony Evers and state Attorney General Josh Kaul, both Democrats, have said they will not enforce the law, and the latter has filed a lawsuit alleging that the law is unenforceable. That suit is expected to eventually make its way before the state Supreme Court.

Kelly, who has refrained from saying how he would rule in such a case, was endorsed by three groups that oppose abortion rights and provided counsel to another Wisconsin group that opposes abortion rights.