The issue came up in passing in a lawsuit seeking to give prisoners the right to vote. While the United States Court of Appeals for the Second Circuit rejected that request, it did express interest in the argument that counting inmates upstate dilutes the voting power of minority groups in urban districts, and kicked that matter back to the District Court for consideration.

The case may provide a roadmap to future challenges.

The 8-to-5 appeals court decision opens a "small window," said Juan Cartegena, general counsel of the Community Service Society, which joined the appeal.

"It's an opening that we really don't know what to do with yet," he said.

Peter Wagner, executive director of the Prison Policy Initiative, a Massachusetts-based research and advocacy group, suggested that wherever the window leads, the mere mention by the court seems meaningful.

"I think it is a significant signal that the New York's reliance on bogus census counts of prisoners creates a serious problem for democracy," he said. "The court has given us a great opportunity."

Noting that the same appeals court also ruled that an inmate whose home was in California but is imprisoned in New York does not have standing to sue here, Mr. Wagner added: "He remains a resident of California, much like the 43,760 residents of New York City incarcerated upstate remain residents of New York City."