An unlikely pairing between organized labor and one of its most ardent foes is emerging in Washington, as players from all sides of the issue jockey for seats around the healthcare reform debate table.

Andy Stern, president of the Service Employees International Union, is joining forces with Wal-Mart Stores Inc. in the oddest coupling since Oscar and Felix shared an apartment, according to the Wall Street Journal (subscription).

The world’s largest retailer is, in the words of the Journal, “a company most labor officials cite as their anti-union poster child.” But in a joint letter by Stern and Wal-Mart sent to the White House June 30, the two urged a mandate that employees provide health insurance to their workers.

It’s a controversial move for the retail giant and a coup of sorts for the SEIU. Most large companies oppose an employer mandate and other large unions remain squarely in the anti-Wal-Mart camp (especially when it comes to its record on labor relations):

“AFL-CIO’s assistant to the president, Gerald Shea, called the SEIU-Wal-Mart letter “a breakthrough moment,” though he said Mr. Stern’s involvement did “raise some eyebrows,” and the labor federation still has some concerns about Wal-Mart’s labor practices.

“James Hoffa [Eds. note: Yes, that James Hoffa], president of the International Brotherhood of Teamsters union, is more critical. ‘We’re not too happy with Wal-Mart. We don’t think they should be an example of how to fix the health-care problems in America,’ Mr. Hoffa said. Wal-Mart, he said, has closed shops where unions have won organizing elections, kept wages artificially low and provided subpar health insurance that is too pricey for many workers. ‘We have a good working relationship with the SEIU on many, many issues, but on this issue we have a different approach,’ he said.”

And it’s something of an about-face for Stern and his union, long vocal critics of Wal-Mart that helped start Wal-Mart Watch, a website devoting to bashing the company.

Strange bedfellows they may be, the alliance is logical from one standpoint: With 400 people working full-time on healthcare issues and a major stake in the outcome, the SEIU would be foolish to eschew the support of one of the world’s largest corporations — and the entrée it affords into the Beltway’s inner sanctums, where that outcome will ultimately be decided.