A major Democratic super PAC is rolling out a seven-figure ad campaign in Wisconsin defending Sen. Tammy Baldwin Tammy Suzanne BaldwinKeep teachers in the classroom Cher raised million for Biden campaign at LGBTQ-themed fundraiser Democrats seek balance in backing protests, condemning violence MORE's (D-Wis.) voting record on taxes, after a conservative group accused her of backing tax hikes.

The Senate Majority PAC, a group run by allies of Senate Minority Leader Charles Schumer Chuck SchumerJacobin editor: Primarying Schumer would force him to fight Trump's SCOTUS nominee CNN's Toobin: Democrats are 'wimps' who won't 'have the guts' to add Supreme Court seats Republican senator says plans to confirm justice before election 'completely consistent with the precedent' MORE (D-N.Y.), is launching the television and digital ad campaign, which totals over $1 million.

It targets Freedom Partners Chamber of Commerce, a conservative group backed by the Republican mega-donor Koch brothers, which announced a $1.7 million ad campaign last week taking aim at Baldwin for protecting special interests and tax increases.

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“There's a reason out of state billionaires are smearing Tammy Baldwin," the new Senate Majority PAC ad says. "They’re protecting the rigged system that only works for them.”

“This time, they want a new Republican tax plan that benefits the top 1 percent — but leaves Wisconsin behind. We know Sen. Tammy Baldwin has voted over 50 times to cut taxes for the middle class. Tax cuts that work for child care, education and retirement.”

Baldwin, who is in her first term in the Senate, is up for reelection next year in a state narrowly won by President Trump in 2016.

The dueling ads on Baldwin's voting record on taxes come as congressional Republicans and the White House push to pass a sweeping series of tax cuts by year's end. House Republicans are expected to unveil their tax legislation Wednesday.

Trump and the GOP have argued that the tax cuts are necessary to accelerate economic growth. But critics say the plan would ultimately be a windfall to the wealthiest Americans.