WASHINGTON — A conservative group known as one of the biggest players in last cycle’s dark money game has launched the first outside attack ad against Sen. Al Franken.

American Encore’s reported $250,000 ad buy looks to tie Franken to a rule proposed by the IRS last fall to define how much “social welfare” groups (also known as 501(c)(4)s, for their tax-exempt status) can spend on political activities. Under current regulations, these groups are supposed to make social welfare their “primary” goal, as opposed to political endeavors like issue-based advertising (The Washington Post explains the proposed rule here).

The ad says the rule is “designed to control the speech of certain non-profits.”

“Sen. Franken pressured the IRS to target these groups. He thinks that free speech should depend on who is speaking,” the ad says over video of a Tea Party rally, “and wants the IRS to make that call.”

Here’s the ad, via the Wall Street Journal, which first reported the buy:

The ad is based on a letter Franken and six other senators wrote to the IRS in 2012 asking it to define what counts as social welfare and political activity for these groups. The letter suggested the IRS, among other things, define what “primary purpose” means for the sake of how much a group should be spending on social welfare versus political activities and require the groups to document, as a percentage, how much they’re spending on each.

The IRS announced its rule change — which has not yet been approved — last November. It would affect groups like American Encore, which, according to the Wall Street Journal, was formerly called the “Center to Protect Patient Rights.” While CPPR didn’t directly spend money on political activities, between 2009 and 2012, the 501(c)(4) group distributed more than $167 million to non-profits that would report political spending, according to the Center for Responsive Politics. (ProPublica detailed the flows of money to and from CPPR during the 2012 election cycle.) CRP has called the group “an ATM for politically active nonprofits on the right” and “the linchpin in one of the most complex networks of dark money in the country.”

Democrats have tried to make outside political groups and their financial backers an issue ahead of the 2014 elections. Franken himself is a big critic of the Supreme Court’s Citizens United decision, which opened the door to more campaign spending from corporations and labor groups. In a statement, his campaign spokeswoman Alexandra Fetissoff called the ad’s claims “ridiculous.”

“Sen. Franken is one of the most vigorous defenders of free speech in the Senate,” she said. “These attacks have been repeatedly proven false. We’ve always known that Sen. Franken was going to be a target of special interest groups. It’s no surprise that they’re here, but it’s not going to stop him from doing his job.”

Devin Henry can be reached at dhenry@minnpost.com.