Hillary Clinton's campaign communications director mocked conservative Catholics and evangelicals in leaked emails from 2011 released on Tuesday.
The messages are part of a reported batch hacked from Clinton's campaign manager John Podesta, with thousands more to come. The Democrat's communications director Jennifer Palmieri and Center for American Progress (CAP) fellow John Halpin allegedly made the comments in an email chain titled "Conservative Catholics" released on WikiLeaks.
"They can throw around 'Thomistic' thought and 'subsidiarity' and sound sophisticated because no one knows what the hell they're talking about," Halpin wrote to Palmieri and Podesta.
The emails date from 2011 when Palmieri was also at the CAP. Now in charge of Clinton's press relations, she suggested news mogul Rupert Mordoch and Wall Street Journal editor Robert Thomson were Catholic because it is "the most socially acceptable politically conservative religion".
"Their rich friends would not understand if they became evangelicals," she wrote.
Halpin said this was an "excellent point".
He earlier said: "Many of the most powerful elements of the conservative movement are all Catholic... It's an amazing bastardization of the faith.
"They must be attracted to the systematic thought and severely backwards gender relations and must be totally unaware of Christian democracy."
Catholic groups reacted with outrage to the leak and called for Palmieri to resign.
"Everyone has a unique faith journey, and it's just insulting to make blanket statements maligning people's motives for converting to another faith tradition," said Brian Burch, president of the politically conservative Catholic Vote group.
"Had Palmieri spoken this way about other groups she would be dismissed. Catholics will be watching Hillary Clinton to see whether she thinks our religious faith should be respected, or whether it's fair game to mock us."
The Catholic League, an anti-defamation charity, also criticised the exchange.
"These anti-Catholic remarks are bad enough but it makes one wonder what else Clinton's chiefs and others associated with the campaign are saying about Catholics and Catholicism," a statement read.
Clinton's campaign has not commented.
