Federal prosecutors are insisting that they properly labeled a prominent Muslim advocacy group, the Council on American-Islamic Relations, as a participant in a criminal conspiracy to support Hamas. In a brief filed Tuesday night, prosecutors asked Judge A. Joe Fish in Dallas to reject an unusual motion from the council, also known as Cair, to strike its name and the names of all other groups and individuals from a list of unindicted co-conspirators filed in late May during the lead-up to the trial of five men on terrorism support charges. The men, all of whom were officials of the Texas-based Holy Land Foundation for Relief and Development, went on trial before Judge Fish in July on terrorism-support and other charges.

Prosecutors said their decision to list Cair as part of the Hamas network was legitimate because evidence presented at the Holy Land trial has included a memorandum describing the group as part of the “U.S. Muslim Brotherhood’s Palestine Committee” and indicating that the purpose of the committee was to support Hamas. The prosecution also noted that an FBI agent testified that two founders of Cair, Nihad Awad and Omar Ahmad, attended a 1993 meeting in Philadelphia that prosecutors contend was a gathering of Hamas backers opposed to the Oslo accords reached earlier that year between Israel and the Palestinian Liberation Organization. “Cair’s participation as a joint-venturer and co-conspirator is a matter of public record in this case,” a prosecutor, James Jacks, wrote.

Justice Department regulations discourage the naming of unindicted co-conspirators in court filings and suggest that when naming is necessary prosecutors file such pleadings under seal. Prosecutors told Judge Fish that he lacks the power to enforce those rules and that sealing was not required, as Cair’s links to the case were about to become evident.

“Because the Government intended to immediately introduce evidence at trial in support of the co-conspirator status, which it has done, the government did not seek to file the Attachment to its Trial Brief under seal,” Mr. Jacks wrote. He also questioned Cair’s claim that the designation had hurt its fund raising and membership, noting that the reported declines took place before the co-conspirator filing in May and were publicly denied by Mr. Awad, who now serves as Cair’s executive director.

An attorney for Cair, William Moffitt, said the government’s arguments were flimsy and amounted to guilt by association. “We’ve looked at the paper and we’re almost laughing at it,” he said. “You have a group with numerous people all doing different things. They take two people who did something together and all of a sudden it means they’re all members of Hamas. Can you imagine where that would have taken us back in the era of the NAACP? On that theory because I have Mao’s Little Red Book in my library that makes me a communist.”

While Mr. Jacks noted that evidence about the Philadelphia meeting was aired at another Hamas-related trial in Chicago earlier this year, Mr. Moffitt pointed out that the government brief omitted a noteworthy fact: The defendants in that case were acquitted on the terrorism conspiracy charges at the core of that prosecution. “They tried to make that a Hamas meeting,” the defense attorney said. “It didn’t fly before a jury of 12 citizens.”

In the end, Cair’s motion may fail simply on procedural grounds. While a founder of the group’s Texas chapter, Ghassan Elashi, is one of the men on trial in Dallas, Cair itself is not a defendant and its legal standing to file motions in the case is uncertain.

The government’s naming of Cair and other American Muslim groups as co-conspirators in the Holy Land case was reported first by The New York Sun.