Workers at a St. Paul Aldi store are slated to vote next month on whether to unionize in a rare labor challenge to the discount retailer.

Like Wal-Mart and Target, Aldi has been busy expanding its U.S. grocery business. But unlike the two retail behemoths, Aldi has drawn little resistance from supermarket unions.

Next month's vote involves only a dozen workers at an east St. Paul Aldi store who will decide whether to join United Food and Commercial Workers (UFCW) Local 1189.

But any union elections at the more than 1,000 U.S. Aldi outlets are exceedingly rare. "This would be the first one I know of," said Bernie Hesse of UFCW Local 1189.

Aldi, a German company with U.S. headquarters in suburban Chicago, couldn't be reached for comment.

The Twin Cities' largest supermarket, Cub Foods, has long been unionized, as have most chains owned by its parent company, Eden Prairie-based Supervalu Inc. And Supervalu's traditional national competitors, Kroger and Safeway, are largely unionized.

But Wal-Mart, the nation's largest grocer, and Minneapolis-based Target aren't unionized, leading the UFCW to vociferously oppose the former for decades, and the latter in more recent years. This week, an administrative law judge ordered a new UFCW union election at a New York Target outlet, citing unfair labor practices by the company.

Aldi, which has 29 Minnesota stores, mostly in the Twin Cities, has met little opposition -- even though the deep-discount chain has been expanding rapidly.

But it's not near the grocery force of Wal-Mart or Target, Hesse said. Aldi stores are often only one-third the size of traditional supermarkets and offer far fewer products.

Small, ultra-low price chains like Aldi on average garner only about a 2.5 percent market share in the cities in which they operate, said Jim Hertel, a managing partner with supermarket consultant Willard Bishop.

Plus, while Aldi employs thousands nationally, an individual Aldi store usually has only 12 to 15 workers, compared with about 150 for a good-sized Cub. Thus, the return on resources for a union organizing drive is considerably smaller.

"We have to start somewhere," Hesse said.

Mike Hughlett • 612-673-7003