A kosher meatpacking plant in Iowa that was the target of a sweeping immigration raid this year is not the only venue where the plant's owners are locked in a fight over undocumented workers.

Agriprocessors Inc. has gone all the way to the U.S. Supreme Court to urge the justices to reconsider their long-held position that workers in the country illegally have a right to join labor unions.

The Supreme Court has yet to decide whether to take the case, but if it does, it could have ramifications for a complicated area of U.S. labor law.

At issue are rules that make it a crime for a company to hire illegal immigrants, yet simultaneously protect those same workers from retaliation for engaging in union activity.

Those intertwined standards came into play at Agriprocessors' small distribution facility on the Brooklyn waterfront in 2005, when a group of about 20 workers voted to join the United Food and Commercial Workers Union.

Agriprocessors fired most of the workers after the vote, saying it had investigated their Social Security numbers and concluded at least 17 were in the country illegally.

The company also refused to accept the unionization vote, arguing that it was invalid because of the workers' immigration status.

The National Labor Relations Board sided with the union and took the company to court. The company ultimately gave the workers $2,500 apiece to settle their retaliation complaints, but the dispute over whether the warehouse is now officially a United Food and Commercial Workers Union shop is still unresolved.