A US federal judge is weighing the fate of a Chasidic rabbi who is citing Talmudic law as a justification for his refusal to testify against fellow Jews before a Los Angeles grand jury investigating tax evasion.

Moshe Zigelman, who was the executive assistant to Grand Rabbi Naftali Tzi Weisz of the Brooklyn-based Spinka sect of Chasids, received a two-year sentence in 2009 after he pleaded guilty to arranging illegal donations.

He had been arrested in 2007 as part of a wide-ranging federal probe into tax evasion in the Spinka sect.

According to federal prosecutors, donors made contributions to the sect which were then refunded, but the donors were able to take up US tax breaks on the back of their supposed contributions.

The Spinka sect took a small cut of the fraudulent donations, prosecutors said.

Zigelman, 64, received a heavier sentence than another defendant because of his reluctance to testify against his fellow Jews.

After his release, the Department of Justice again sought his testimony before the LA grand jury that is investigating other aspects of the alleged scheme. According to the Los Angeles Times, Zigelman is citing "mesira", the Talmudic doctrine that bars Jews from informing on other Jews to secular authorities, in refusing to testify.

His lawyer, Michael Proctor, wrote in court papers: "No earthly sanction will ever make Rabbi Zigelman abandon his religious precepts."

A spokesman for the US attorney's office in Los Angeles said he couldn't comment because the matter was before a grand jury, which is a secret proceeding. Judge Margaret Morrow of the US District Court in Los Angeles heard arguments in the case last Wednesday and has said she will rule at a future date.

Michael Broyde, professor of law at the Emory University School of Law in Atlanta and a member of the Beth Din of America, said Zigelman was probably on shaky ground from the court's perspective. "I don't think there is any legal justification from a US law perspective," he said.

He said the classic Talmudic prohibition that Zigelman cites is rooted in the notion that Jews should not betray their fellow Jews to an evil government, and its relevance to a more just government is not clear-cut.

But he said Zigelman's situation is complex from the perspective of Jewish law. "We all see criminal activity within our own community and we avert our eyes because there's no obligation to call the police in the United States," he said. He added that the only "mandated reporters" such as police officers or child welfare caseworkers are obliged to report incidents to the police.