In an unusual beer bust, state investigators recently spotted a Maple Grove bar illegally tapping a popular Wisconsin beer after a border run to get it.

Undercover officers busted Maple Tavern for selling New Glarus Spotted Cow, a farmhouse ale that can only be sold in Wisconsin — a felony criminal offense.

In a search warrant filed in Hennepin County, the state Department of Public Safety said it was tipped off to the alcohol-related crime by the Wisconsin Department of Revenue, which was notified by an anonymous complaint. According to the search warrant, Maple Tavern’s manager made beer runs to get six Spotted Cow kegs for retail sale from a liquor store in Hudson, Wis., from Feb. 20 to April 4.

But investigators from the state’s alcohol and gambling enforcement division didn’t need to go far for confirmation; Maple Tavern’s own Facebook page showed a photo of a Spotted Cow tap handle, court documents said. Investigators confirmed the purchase at the liquor store and then went right to the source itself — ordering a glass of Spotted Cow at Maple Tavern to collect the evidence.

Beer manufactured by New Glarus is only distributed in Wisconsin. The company is not a licensed manufacturer of alcoholic beverages in Minnesota, so it’s illegal to distribute New Glarus beer to a retail establishment. Neither the bar’s manager nor the Maple Tavern are licensed to transport or import alcoholic beverage into Minnesota.

At New Glarus’ brewery, where the motto states “Only in Wisconsin!”, the website says “You know you’re in Wisconsin when you see the Spotted Cow.”

“It was a mistake, but it was the best of intentions,” Brandon Hlavka, another manager at Maple Tavern, said about bringing the popular Wisconsin beer there.

At New Glarus, co-owner Deb Carey was baffled by the news. She said similar situations have happened twice before — in Illinois and New York.

“We’re really flattered he’s gone through all this trouble,” she said of the Maple Grove bar. “It’s baffling to us, too. There’s a lot of great beers — there’s a lot of great Minnesota beers. For someone to go to this length, I don’t get it.”

The brewery has quite a passionate following and now produces 190,000 barrels of beer a year — the top craft brewery in Wisconsin. And yet, Carey said there are no plans to expand into the neighboring state, or anywhere else.

“Our goal has never been to be a big brewery,” she said.

The case remains an active investigation, so state Department of Public Safety spokesman Bruce Gordon couldn’t comment on the case Monday, but he said that this is the second such criminal case in the past five years. In 2011, Stadium Bar and Grill in White Bear Lake was charged for importing alcohol across state lines from Wisconsin, and the owner pleaded guilty.

In the Maple Grove case, charges haven’t been filed yet. It’s a felony to transport or import alcoholic beverages for resale unless it’s from an alcohol wholesaler, manufacturer and/or brewer.

At the Hudson liquor store where the Maple Tavern manager went, Historic Casanova Liquor, an employee said Minnesotans flock there for Wisconsin beer since it’s the closest to the border, with Spotted Cow as its No. 1 seller.